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May 27, 2010

Sony EX71

It's not fair. Why do these in-canal phones have such sweet bass but leave something to be desired at the higher frequencies? And why the anomalies in testing/listening?

In a head-to-head (heh) comparison with the Etymotic ER6i, the EX71s sounded richer and deeper in the bass, but that's not how my instrumentation saw it. It told me that the Etymotics went deeper and had flatter frequency response. Time for a closer look.

And so the frustration begins of trying to get meaningful, much less repeatable, information when doing audio testing. One of the biggest variables is how an in-canal transducer sits in your ear. It's never the same twice, and my testing involved a lot of switching back and forth, using only one rubber ear, because I didn't want another variable (a different microphone) to enter the equation.

This first run is smoothed response to pink noise from the ER6i in red, and the EX71 in blue:

Both phones are being driven from an Archos PMA430, a player with a strong output stage that's not intimidated by low-impedance headphones. Both the EX71s and the ER6is are nominally 16 ohms. I made both measurements without changing the volume level on the player or the gain on my instrumentation.

You can see that the ER6i response is very smooth, while the EX71 is kind of bumpy. Those little stairsteps on the top end of the ER6i curve are distortion artifacts, by the way. The Archos player is distortion-free, which is another reason to use it as a source for testing like this. The distortion appears to be harmonics generated in the earphone transducer. But it's unimportant in this test anyway.

Looking at these curves, the EX71s are clearly not as efficient, and the midrange hump is sure to color the music.

I took another shot at these measurements, turning off smoothing and reinserting the transducers in the measurement ear:

This time I didn't get distortion from the ER6i at the high end, but it picked up a little 800Hz bump, probably because of slightly different location in the ear. The Sony, meanwhile, looks pretty much the same, except that it's actually doing better in the high treble range. It's also picked up some 60Hz hum. I tried to eliminate it or figure out what appliance or piece of equipment was generating it, but no dice. It's just a bump, however; draw a mental line through it.

On this third run, I used my sound level meter to set the in-ear loudness the same on both earphones, figuring that if one was quieter than the other, you'd naturally turn it up to your preferred level of enjoyment. Both of these runs were at 78dB in-ear loudness. My onscreen instrumentation read the same input level for each, too.

Equalizing the volume tells a different story. Both earphones show a peak in their response curves, and now the Etymotic run has caught the 60Hz disease. But the important thing is that when equalized for loudness, the Sonys are stronger in the bass range.

Back here in the real world of listening, the EX71s definitely have more thump than the ER6is, and nowhere near the extended top end of the ER6is. So don't believe everything you see on a computer screen.

Blocking out noise
The EX71s are typical of most in-canal earphones, and my meter shows an average reduction of 10dB. You can see the attenuation of the actual frequencies here:

The blue line is white noise in my testing room. The red line is what my measurement ear hears with the EX71 inserted. They do a good job in the midbass, but flanged designs seem to have a penchant for letting 1KHz through. They get a lot better in the high end. This performance is somewhat surprising, considering that the EX71 is a single-flange design that doesn't go very far into the ear.

These are very comfortable earbuds; they rest lightly in the ear, but don't tend to fall out. They fit very small ears well, which is sometimes a problem for in-canal phones. This measurement ear was molded from a small woman, and is very petite:

The EX71s come with two different eartips for smaller and larger ears, a hardshell case, and a unique, smaller, cylindrical case that you snap the earbuds into.

The cylindrical case prevents the earbud leads from knotting up around one another and protects them. The left cord is shorter than the right, something that has become fashionable among some earphone manufacturers. I dislike it; I'd rather have them equal length so that the cord stays centered and doesn't tug on just one ear.

The Sony EX71s are a rock-'n'-roller's ear canal phone. I haven't encountered another in-canal phone with as much bass. They're very small, very comfortable, and don't attract the "mug me" attention of The White Earbuds. They don't exert the pressure on your ear canal that you get from the phones that go deeper. They also don't deliver the crisp, laser-sharp highs of the Etymotics, but at $50 or less, they're a good trade-up from your everyday earbuds.

Posted by machrone at 10:30 AM | Comments (7)

May 26, 2010

4th-generation iPod

What can you say about the world's most popular digital audio player? How about, "It could be better."

The 4th-generation iPod is the player that all others are compared to for ease of use, style, and substance. It's more than just an audio player; it's a platform, with hundreds of accessories and add-ons to tailor it to your needs. While other manufacturers have added FM radios, recording, and other features to grab just a bit of the iPod's market share, Apple has resolutely held to its music-only stance. (The iPod photo is a different model, aimed at a different user.)

The iPod's audio performance should be as iconic as everything else about it. Unfortunately, it's not as consistently wonderful as the rest of the player.

If you don't use EQ on the 4th Generation iPod, everything's generally fine. When you turn EQ on, things are not so fine. But even without EQ, the iPod could--and should--have more bass.

Here's the frequency response with the standard white earbuds plugged in:

It has the typical audio player droop in the bass, mostly caused by headphone loading on the single-ended, capacitor-coupled output circuit. Down 5dB at 40Hz, down 10dB at 20Hz? That's a lot of bottom end to give up.

The harmonic distortion in the iPod 4G is acceptably low with no EQ. You can see a single harmonic in the bass, and it comes back again in the treble. But it's way below audibility:

When you select bass boost, however, it's not really boosting the bass, it's piling on harmonics in the bass range:

When your brain hears more harmonics in the bass, it thinks it's hearing more of the fundamental. It's a nice psychoacoustic trick, but in fact it's blurring the bass notes and lending an unrealistic timbre to the instruments. When you listen to the sweep tones, you can hear the difference--a nasal timbre instead of the purer sound of the sine wave. The stuff over on the right is low-pitched hissy/poppy noise as the sweep tone goes through the mids and trebles.

Now let's try another EQ preset, this time the Jazz setting:

Look what they've done to my song, Ma! We've got a nice stack of harmonics in the midbass to midrange, but complete chaos in the treble. Something inside the iPod has hit the analog or digital wall, and is now spewing subharmonics. When you hear a note like this, say a violin holding a note, you hear the note, EEEEEEEEEE, and behind it you hear sssshhhhrshhhshhhhshhsrrrhsh. It's 30 and 40dB below the note, but it's there. The distortion-plagued sweep tone itself sounds like a catfight played over an old AM radio.

I'm pushing the player pretty hard, however. The earbuds are cranking out 90 to 100dB of in-ear volume during this sweep. So let's back it off to a more comfortable 85dB in-ear:

Ahhh, that's better. There's one lone gothic arch in the treble and a very faint harmonic in the midrange. The question is, is 85dB in-ear loud enough for your listening enjoyment, and how quickly does the distortion get bad when the loud passages come along or when you crank it up a little?

I don't want to vilify the iPod too much. It's a fine-sounding player most of the time. But it's also just a couple of volume clicks away from serious distortion if you use the EQ. Each of the settings behaves a little differently, but they all exhibit this behavior, sprouting hair and growing fangs as the volume goes up.

One final torture test. This is the iPod's unloaded 40Hz square wave, which looks pretty darn clean:

But when you add the earbuds, it's like a kid playing the tuba--not enough air to sustain the note:

The result is that droopy frequency response curve we saw at the outset.

There's a moral to this tale. Several of them, actually. One is that you don't need to be great to be good. The iPod's fidelity is more than satisfactory for the vast majority of users, especially in the noisy commuting, exercise, or travel environments. The second is that 32-ohm earphones really stress the player. It performs better and sounds better into higher-impedance phones. Unfortunately, earbuds and in-canal phones tend to go the other way, to lower impedance, in an attempt to suck more power out of the player. Equally unfortunately, there's not enough power there to satisfy their craving at the low frequencies.

The iPod with my 64-ohm Sennheiser HD280 Pros is sweet--bass is vastly improved, and the efficiency of those big cans means you hardly have to crank the volume. You stay well away from the distortion zone.

If you really want to hear what the iPod can do, use high-bitrate compression or lossless compression and play it into your stereo. The high-impedance load preserves all of the iPod's fidelity, even with the EQ on. And if you want startling fidelity when you're on the go, with headphones of any type, invest in a headphone amplifier. About the size of an Altoids tin, these things can crank up to half a watt into your headphones. Not that you need that much, but they offload the iPod's load-sensitive output stage and do all the heavy lifting.

You don't need a headphone amp when you're jogging or in other noisy environments, but when you want to get down with your music, it elevates your iPod to its fullest potential.


More to come....

Posted by machrone at 01:36 PM | Comments (3)

May 25, 2010

Archos PMA430

Calling the Archos PMA430 a digital audio player is like calling a Swiss Army knife a can opener. It's all that, but it's much more, too. In addition to digital audio, the PMA430 also does video and is a photo viewer. It records line in or microphone, and records video, complete with a timer to catch your favorite show or movie. It also has a fairly functional PDA, and the color screen is touch-sensitive, with handwriting input and a pop-up keyboard. It's also a USB host, so you can download pictures from your digital camera.

And if that weren't enough, it has built-in WiFi and an Opera browser, so you can download new songs, check the news, and do your email while you're sitting in Starbucks! But this is the Serious Personal Audio site, and if the PMA430 didn't do great audio, I wouldn't be talking about it--or at least not in such positive terms.

As you can see from the list of capabilities, the PMA430 is in a different class than music players. It's bigger and heavier (10 ounces instead of the usual 4 to 6), but the color screen is large enough and sharp enough that you can watch movies enjoyably, and the touch screen beats buttons, scroll wheels, and all the other audio player user interfaces. It costs more, too. But the extra features may make the $600-plus price worth your consideration.

The display screen while music is playing is complete and informative, without silly animations such as those on the the Toshiba gigabeat, and you can pop up the EQ window at any time, browse to another selection, or use PDA functions.

Overall audio performance is impeccable, with lots of power on tap. Headroom is important in audio for realistic performance when peaks and crescendos come along. It's also critical to good bass performance because low-impedance headphones tax the player heavily. The PMA430 drove my loudness test track to an undistorted 107-110dB through the provided earbuds, with peaks of 118dB. That's painfully loud, and nobody turns it up that high (at least I hope not). But the extra power is there when it's needed, and lets the PMA430 sound lively and unconstrained.

Freequency response is reasonably flat throughout the range, although with the usual bit of droop at the bottom end from headphone loading. Still, the droop is less than any other portable player I've yet encountered:

You can also see a little wrinkle in the midbass performance, a 1-2dB boost which adds a slight warmth. It's not perfect performance, but it's not objectionable either.

The PMA430 is one of those rare players that adds no harmonic distortion when you boost the tone controls or use the EQ presets. This spectrogram shows the performance with the EQ set flat:

And this one shows bass boost:

The bottom end basically gets louder, period. That's the way they should all be. These spectrograms also reveal the source of the additional warmth in the midbass--a bit of harmonic distortion that's around 50dB down, but still adds up to the small bump in frequency response. As I said before, though, it doesn't detract in the slightest from the listening enjoyment you get from this player.

Another way of looking at the bass performance is with the 40Hz square wave test. This one pushes players to the wall, asking their output sections to provide large amounts of current accurately.

Here's the PMA430's raw performance, with no headphone load:

This is about as clean a square wave as you could hope for. It's the product of good audio engineering and a well-regulated power supply.

When I plug in the 32 ohm earbuds, the waveform droops, but less so than in any other player I've encountered. This is confirmed by the octave band sweep and by listening tests--the bass performance is delightful!

The PMA430 is also unusually quiet. As you can see in this sweep test with the sweep active, the inactive parts of the spectrum are down at the noise floor, 100dB below the signal.

Thus the sounds you hear emerge from a background of silence, not hiss or burbles or some of the other noises that plague digital audio players. Again, a testament to good design and construction.

If you're an iTunes devotee, you can download a plug-in from the Archos site that lets iTunes recognize the PMA430. It can't play AAC files, but you can use iTunes to manage your MP3 music. iTunes organizes the music slightly differently than the Archos default, but it's not a problem. Frankly, it's easy to just drag and drop WMA and MP3 music to the Archos and let it sort things out; I drag music right out of the iTunes folders rather than letting it write to the PMA430.

Audio geek or not, I can't ignore all the other things that the PMA430 does, especially since it does them so well. As a photo viewer, it's one of only a few (the Archos Gmini 400 and the Epson P2000) that can zoom in on photos and pan around. It's a great feature, very useful for showing others details and points of interest in your pictures.

When you want to record TV, you drop the PMA430 into its AV dock:

The dock has a short umbilical cord that plugs into the side of the player. Everything else plugs into the back of the dock--line in/out, video in/out, S-Video, power. The dock has a nifty swivel base that holds the PMA430 straight up or angled back for best ease of use in your installation.

The PMA430 records video at 512 by 384 pixels, in MPEG4 format. Playback looks roughly the same as VHS on a TV, and looks pretty darn good on the LCD screen. The picture above was captured from the evening news. That's a tiny speaker grille on the front, and you can direct audio through it without disabling the headphone/line output, which can be useful. The dock also comes with a remote control, which gives you complete control over the personal video recorder functions. You can choose manual or scheduled recording. It includes an infrared emitter, which you position in front of your cable or satellite box to change channels. It's programmable from the PMA430, of course.

WiFi connection and setup is straightforward. The PMA430 will find open connections, and will connect to WEP-protected access points if you provide the password, but it can't connect to stealthed access points.

Using the PMA430 as a USB host is easy, too. Just connect any camera that functions as a USB mass storage device, and you're all set. With 30GB, you can put a heck of a lot of vacation photos, even at full resolution onto the 430, and save yourself the trouble of toting a laptop or limiting your photos to the amount of camera memory you have on hand.

The PDA functions are the usual calendar, to-do list, contacts,

More to come....

Posted by machrone at 08:13 AM | Comments (3)

May 23, 2010

Etymotic ER6i

That's et-ee-MOE-tic, not etty-mottic, and the ER6i is Etymotic's most popular model, retuned with greater sensitivity and better low bass performance for the iPod and its ilk, which tend to have lower output than CD players and less oomph in the bass. But low-impedance earphones like the ER6i have, and as you'll see, can cause their own problems with bass.

In-canal earphones like the ER6i have two jobs: deliver good sound and seal out noise. People generally agree that in-canal phones do a better job than earbuds, but how well do they isolate you from outside noise?

Rather well, as it turns out. But I prefer the foam eartips to the three-flange rubber eartips (above) that you usually see on these phones. The three-flange eartips are fine; they're soft and comfortable, they seal out noise pretty well, and they fit a wide range of ears.

The foam eartips are more comfortable for extended wear, however, and they somewhat outperform the white rubber ones. I really like the closed-cell material Etymotic supplies with the ER6i--it compresses easily in your fingers, expands quickly to your ear canals, and doesn't exert undue pressure. Unlike several other foam eartips, the closed-cell foam is smooth. Some of the more open foams, as on the Shure E3c and E4c, are actually kind of rough and abrasive-feeling. They also collect dirt more readily and are harder to clean.

In this photo you can see how nicely molded the foam eartips are, and on the other driver you can see the filter at the end of the sound tube. The filter is a small foam-filled plug that does several things beyond the obvious one of keeping ear wax out of the tube. It provides a bit of backpressure on the diaphragm, which, along with the acoustical filtering properties of the filter, smooths out the frequency response. Without the filters, the ER6is sound harsh and brassy.

I test the frequency response in rubber ears that have been molded from human ears, with calibrated microphones behind them, mounted the proper distance into the ear canal. This is homemade equipment, not a $20,000 anatomically and acoustically correct binaural head. But I've been an electronics and audio hacker all my life, and I think my homegrown rig is pretty good, and definitely yields usable comparative results if not absolute, acoustics lab accuracy.

Etymotic rates the frequency response of the ER6is from 50Hz to 6KHz ±3dB and from 20Hz to 16KHz ±6dB. My measurements are consistent with the ±3dB rating, but depending on what you're driving them with, you may never hear a 20Hz tone from your ER6is (more on this later). My test rig attenuates both ends a bit. but is very consistent in the way it treats headphones, earbuds, and in-canal phones. At 50Hz, the response is at least 10dB weaker than my studio-grade Sennheiser HD280 headphones, but the ER6is catch up quickly and are dead flat across the spectrum. They tail off gracefully at the top end, but audio material with lots of highs is not the least bit constrained.

The ER6is do a decent job of blocking noise. Quoting a single dB figure is pointless since the amount of attenuation varies so much by frequency. So here's a picture of what they actually do:

The blue line is white noise in my testing room, measured through a rubber ear. It's coming from five speakers, and it measures an average 85dB. The red line is what the microphone in the ear with the ER6i equipped with the three-flange rubber eartip hears. As you can see, the attenuation is all over the place, and 1KHz lances right through. My equipment calls it a 10dB average reduction, but obviously it's much greater than that at the higher frequencies.

Here's the same test, but with the foam eartips. Notice how much better the high-frequency attenuation is, along with a couple of dB improvement in the midbass.

Looking at these charts, bear in mind that white noise has a degree of randomness in it, and these traces dance around a fair amount during testing. Your eye averages them out, but what you see when you grab a screen shot may not agree with what your eye was telling you. So I pull the trigger several times and use the one that most closely matches the active, average performance that I see on the screen.

Also, sound reaches your ears in paths other than your ear canals, and these tests don't account for it. Your skull, neck, and upper chest are all entry points.

The ER6is have a wonderful, open sound. They're a pleasure to listen to, but I admit that I'd like more thump in the bass. Piano, violin, and voices sound almost magical; they're clean and well-articulated. Brass is never strident. A jazz drumset is crisp, present, right up front. The lowest notes in the bass are more implied than forcefully stated, however. By contrast the Sony EX-71 in-canal phones have more bass but a lot less definition in the trebles and midrange.

If you wear the ER6is extensively, you'll eventually need to replace the filters. The sound gets dull as they become clogged with dirt and ear wax. Etymotic provides an extra pair, plus a little extraction tool that removes the old ones (destroying them in the process). Replacement filters are not exactly cheap at $12.95 for a pack of six; Q-tips are a wise investment.

In my testing, one of the filters came loose in the sound tube and created a buzzing rattle. I simply pressed it back into place, and didn't encounter any additional problems.

Etymotic increased the sensitivity of the ER6i over the original ER6 by reducing the impedance. I think that this is the wrong solution for most digital audio players, especially those with already-limited bass response. The limited power of digital audio players is a good reason to increase sensitivity--people want their loudness! But low impedance hurts bass response when there isn't power to spare because it just sucks more power out of the player than it can provide.

This quick-and-dirty Excel chart shows what I mean:

This is the performance of the player with two different sets of phones attached, sweeping from 20 to 400Hz. The player was a Creative Zen Micro, which has roughly the same bass performance as a white iPod, maybe a little better. As you can see, the ER6is cause a 5dB fall-off in the bass at 20Hz, down to 3 or so at 40Hz, 2dB at 80Hz, and fading into insignificance above that.

Irrespective of what the earphones can do, if the player can't deliver the bass because it's being loaded down, you're hardly going to hear the sweet lows; they'll be pushed far into the background.

I tried the same thing with an Archos PMA430, a multimedia player with prodigious amounts of audio power. The Etymotics still pulled down the response, but only by about 3db at the lowest frequency. I ran the tests flat, but the PMA430 can dial in large amounts of EQ without introducing distortion. The ER6is welcomed the bass boost.

This interaction between player and earphone is something you need to be aware of if you're looking for brain-compressing bass. Since so many players add distortion when you use their EQ settings, you need to be doubly cautious. The ER6is with a player of the PMA430's caliber are a real pleasure, but those low notes are noticeably "less there" on lesser players than I like.

The wires on the ER6is are very thin, and are prone to "sing" if you walk quickly outdoors or if there's a breeze. The tone is conducted right into your ears, so it's best to insert the drivers upside down, with the wires up, and loop them over and behind your ears if you're outdoors. Etymotic provides a clip so you can secure the wire to your clothing, as well as a nice little soft carrying case.

At their $129 street price, the Etymotics are more or less in the middle of the range for in-canal earphones. They aren't perfect, but they're the best in their price range. If you want to hear what they can really do, invest in or build a headphone amplifier. You'll be amazed.

Posted by machrone at 06:04 PM | Comments (2)

May 20, 2010

Creative Zen Micro

Audio geeks love to hate the Creative Zen Micro.

"It doesn’t look serious enough. White plastic bathtub case? Lollipop face colors—nine of them? Pulsating fiber optic rim light? I mean, come on!"

Get over it.

The Zen Micro is a solid little player with some interesting features. It also has some sonic flaws, but oddly enough, they’re self-healing. I like the touch interface, but it's an acquired taste. Some people hate it. Some people hate the iPod touch wheel, too.

The Zen Micro has the same problem as many other players--very good audio performance when the EQ is off; some nasty distortion when it's on. But when you turn on Smart Volume...

... the distortion magically disappears.

Here's the frequency response of the Zen Micro as I feed it a sweep tone from 20Hz to 20KHz:

It looks pretty good. It's flat, with the usual weakness in the bass, down about 3dB at 40Hz and 7-8dB at 20Hz. It's better than most players. We'll take another look at bass response further along. If there's any harmonic distortion, this view of the player's response doesn't show it, because the loudness of the distortion is lower than the loudness of the fundamental frequency. To see the distortion, we need to switch to another view. Here's the spectral view of the same 20-20KHz sweep tone, with the EQ off:

This is clean, listenable performance. There's not a hint of harmonic distortion. The transition from red to orange at 40Hz and below shows the weakness in the bass that's typical of virtually all digital audio players, but it's tolerable.

Now let's turn on the EQ. This is the Rock EQ setting at a volume level of 23 (out of 25):

Nice, huh? Those bands over the bass side are harmonics. Some audio designers think this is an OK way to boost some frequencies: fool the ear by adding harmonics, but don't make the fundamental frequency any louder. Psychoacoustically, it kind of works. When your brain hears a 120Hz tone added to a 60Hz tone, it perceives that the 60Hz fundamental is louder. But if you listen carefully, you'll also hear that the fundamental is blurred and that the sound is no longer an accurate representation of what the instrument sounds like.

Those cathedral-like traces in the high frequencies are wolf tones. They're the result of some electronic component being driven beyond its capabilities or the product of a harmonic above the test tone combining with the test tone to create a beat frequency that's harmonically unrelated to the fundamental. They sound like you're tuning an old radio between channels--squeals and hisses. As a result, the Rock EQ setting sounds like you've stuffed cotton in your ears, or that there's a blanket over the music. It's literally become smudged and blurred.

Then you turn on Smart Volume, and tranquility reigns again:

What's going on here?

The Zen Micro documentation describes Smart Volume as a volume leveler, which equalizes the volume within a track, making the quiet passages louder and keeping the loud passages from getting too loud. It also equalizes the volume from song to song, so you have less need to reach for the volume control as you move through your playlist. Circuits that do this have been around for 60 or 70 years, and are called limiters or automatic gain controls. If Smart Volume were nothing more than an AGC, it would just introduce more sonic flaws. It wouldn't be interesting--and it wouldn't do what you see on the screen above.

I talked with Dr. Lee Morse, an audio scientist at Creative about Smart Volume, and learned that it's a patented algorithm that Creative uses in a number of its audio devices, including sound cards and the Zen Xtra. Far more than being an AGC, it actually looks a frame ahead of the codec at the music and gives the codec hints of what's coming so it can do a better job decoding it accurately. Moreover, it stores the hints in the metadata tag area of the file so it can do a better job next time. That's right: When Smart Volume is on, the selection will sound better the second time you play it.

Creative came up with Smart Volume because they wanted to maximize audio quality and improve listenability in noisy environments without coloring the music; eliminating distortion in the EQ settings was apparently a surprise. Morse speculated that it may be attributable to switching to 32-bit arithmetic in the DSP when Smart Volume is turned on.

There have been reports that Smart Volume cuts into battery life. Morse agrees that this could be the case because it uses extra CPU cycles. I haven't done rundown tests yet, but it appears that it could be shaving half an hour off the total runtime of the Zen Micro.

So how does it sound? Fine by me. The Zen Micro will still pump 100dB into your ear canals through its stock earbuds at a setting of 23 out of 25 on the volume control, with zero distortion. My test tones measure significantly quieter, but music is only off the no-Smart Volume peak by about 5dB. Here's a picture of the sweep tone with Smart volume on and no EQ:


The volume leveling is evident on my favorite loudness test, Boston's "More Than a Feeling," which is notable for having a remarkably well distributed sonic spectrum, better than most full-on orchestral music because of the electric bass line and the incessant cymbals. The song begins with a fade-in of an acoustic guitar, which is noticeably, but not irritatingly louder than when Smart Volume is off. The peaks in the songs chorus are reined in, and only jump up 2-3dB instead of the more usual 5-6dB. Again, it's not enough to ruin your enjoyment, and it's handy when you're just doing casual listening, especially in a noisy environment.

More to come....

Posted by machrone at 09:34 PM | Comments (4)

iPod mini 6GB

A new hard drive, 50 percent larger. New colors. Better battery life. New audio performance? The original iPod mini caused quite a stir when it was introduced, but the audio performance, especially in the bass, left something to be desired.

Actually, it left a lot to be desired.

Audio enthusiasts complained about the bass response right from the outset, even as people snapped up minis by the millions. Hey, I've got one. And I don't regret it one bit. Weak bass or not, it's been the source of many hours of listening pleasure. The 6GB version of the mini gave Apple the opportunity to right some wrongs, as well as take aluminum anodizing to new heights. The question is, did they?

I breathed a sigh of relief when I ran the first tests on the iPod mini 6GB because Apple had, in fact, addressed the bass performance. It's not stellar, but it's noticeably better than the original mini.

This is the octave-band sweep, snapped while a sweep was in progress. The vertical bars are unimportant; the recorded peaks show the response at each 1/3 octave measuring point.

The amount of droop at the lowest frequencies is typical for players of this class, and is largely caused by the load from the standard iPod earbuds; when the iPod is unloaded or playing into a high-impedance load such as a car stereo or a headphone amplifier, the response is much flatter.

Even with the falloff at the low end, the 6GB mini sounds better than its predecessor. There's more bass there. Switching back and forth between an original 4GB mini and a 6GB with the same earbuds and the volumes set to the same level, there's a subtle, but noticeable improvement.

The 40Hz square wave test is about the harshest thing I could come up with to wring out the bass response. The unloaded response is noticeably better than that of the original mini. Here's the original 4GB mini:

This droopy-looking curve above shows that the original mini can't make a decent square wave even with no load.

The 6GB iPod makes a decent-looking, if not exceptional square wave, a much more promising foundation for bass performance.

The 40Hz curve of the original 4GB mini with the earbuds attached is a complete mess.

The 6GB mini is a big improvement, but the 32-ohm earbuds manage to pull the voltage down to zero by the end of each half-wave. The result: it still runs out of steam in the bass.

more to come....

Posted by machrone at 09:34 PM | Comments (0)

May 19, 2010

Sennheiser PX100

If you don't care about blocking out noise or about the embarrassment of sound leakage--or if you just like the unconfined feel of open-backed headphones, the Sennheiser PX100s are the best lightweight headphones I've yet found. And at $49, they won't break the bank.

The two-inch foam pads sit lightly on your ears, and the phones weigh a mere 3 ounces--easy to carry and easy to wear. They also fold to a convenient size and have a rugged, if complicated, case. But the real story is the audio performance.

The PX100s go almost as deep in the bass as the Sennheiser HD280 Pros, which are my idea of what studio/critical listening headphones should sound like. In my tests, both are flat down to 50Hz, below which the PX100s begin to lose steam. But they're only off the pace by 3dB at 40Hz and 6-7dB at 30Hz.

More importantly, they're dead flat through the rest of the audio spectrum, and they roll off at 13KHz and beyond, following the same gentle curve as the HD280s and the Shure E4c in-canal phones. Since they're open-back, they feel more open and spacious than the closed-back or in-canal phones. They do everything remarkably well for something so small and light.

As you can see from the above chart, they do very little to block out external noise. The blue trace is 85dB white noise in my test room and the red trace is what the ear behind the headphone hears. So don't take the PX100s on your next plane flight expecting to be wrapped in a cocoon of silence. You will, however, hear your material and the plane's audio programming with unaccustomed clarity.

Here you can see the two small cushions on the top band. The taper helps to keep the PX100s centered on your head. They stay in place well enough to jog or work out, without the distracting movement noises that you often encounter with earbuds. If you run outdoors, they're a safer alternative to in-canal phones because you can hear traffic, approaching bears, and the like. Plus, they'll keep your ears warm in winter! My test head has small rubber pinnae (that stick out endearingly), and you can see how the swivel mechanism adapts to keep the earpieces flat against the ear. They work just as well on larger ears.

The swivels turn a full 90 degrees and the sidepieces are notched, so the phones can fold to a very compact profile, as you can see here.

The hinged plastic case is kind of complicated, but strong. After you slide the folded phones into the case, you wrap the cord on a molded channel that keeps it in place. Then you snap the case closed. It's all very Teutonic; the underlying mindset will be immediately familiar to BMW and Mercedes owners.

The PX100s are great little headphones; I can hardly say enough good about them.

Posted by machrone at 10:52 PM | Comments (0)

May 18, 2010

Gateway MP3 Photo Jukebox

Gateway's MP3 Photo Jukebox has excellent audio quality. Surprised? I was. With no background in personal audio devices, Gateway pulled this one out of a hat. It looks a little plastic-y, but don't let appearances deceive you--this is a fine performer that will fill your ears with good music. This latest version is 6GB, up from 4GB.

The Photo Jukebox, as the name implies, also displays photos, but with a 128 by 128 pixel screen, you have to ask yourself why. The color screen is easy to read when the backlight is on, however. More important, I think, than viewing photos is the ability to connect to digital cameras that are USB mass storage devices and dump their contents to its hard disk.

In this photo, you see the Photo Jukebox's least-endearing feature, the bulky combo USB interface and power plug. I greatly prefer standard USB connectors and coaxial power connectors (and charging through USB). But if you can get over the clunky, oversized connector, this is a lot of player for the money.

First, let's look at frequency response:

Any day you see less than 10dB droop at the low end of a digital audio player is a good one, and the Photo Jukebox delivers. It's only 4dB or so down at 40Hz, which is premium performance in this class of audio player.

Looking at the same sweep in spectrogram view, you can see that it's very clean:

You can also see that the Photo Jukebox is not phenomenally loud, lacking the bright red stripe of fundamental frequency that's typical for these graphs. Keeping the volume under control probably contributes to keeping distortion under control. The loudest peak I saw on my loudness test track was 102dB of in-ear volume through the provided earbuds, with average loudness in the 96-98dB range.

Now let's kick in some EQ. This is the Jazz Bass preset:

You can see the low-end boost clearly, with only the faintest hint of harmonic distortion in the midbass/low mids area. Again, solid performance. The original 4GB version of the Photo Jukebox had the same mature behavior, by the way.

The Photo Jukebox did well on my 40Hz square wave test, too. Here's the unloaded waveform:

Clean, with just a bit of overshoot. Now let's plug in the earbuds:

As you can see, the waveform gets pulled low, but not all the way to zero. With a little gas left in the tank, the Photo Jukebox has decent bass response, as seen in the octave-band frequency response graph. Listening to the Photo Jukebox is a pleasurable experience.

The Photo Jukebox is compatible with Windows Media Player 10 DRM, and Napster to Go, so you can either buy or rent music. The controls work smoothly, and the color screen makes the menu selections quite readable. When the backlight goes off, however, the screen is unreadable; you've got to touch a button to light it up again.

On the non-audio side, the Photo Jukebox connects to a long list of cameras that operate as USB mass storage devices. You can dump the contents of the camera's memory to the Photo Jukebox for later upload to your computer. Or, using the Photo Jukebox's internal file manager, you can move some or all of the photos to a folder that you can view on the screen. The 128-by-128 pixel screen is rather coarse for photo viewing, and there's no zoom-and-pan feature. But it's no worse than most cell phone camera screens, so you can at least get a sense of what the photo will look like printed out or displayed on a larger screen.

The battery, by the way, is user-replaceable, so you don't have the iPod hassle of sending it back for replacement when it eventually stops accepting a charge.

If you travel with a camera and appreciate good audio, the Photo Jukebox is definitely worthy of your consideration. Heck, even if you don't travel with a camera, it's a solid audio player in its own right.

Posted by machrone at 11:04 PM | Comments (0)

May 17, 2010

Bass Performance in Digital Audio Players

This article is a companion to my column, "Shuffle's Got a Secret" in PC Magazine.

It's an attempt to quantify the performance differences among several digital audio players. While all have essentially flat (or flat-enough) frequency response with sine wave sweep tones and less than 0.1% THD at 1KHz, there are audible differences when driving professional headphones or self-powered studio monitors. All can drive a standard set of earbuds (in this case, the standard Apple earbuds) to 100+dB in-canal loudness using a rock test track that fills virtually the entire audible spectrum with a constant din.

Most of the difference is in the bass response, but little differences are discernible from one unit to the next with a 40Hz sine wave (roughly low E on the electric bass). After performing many different tests, I came up with the following test tracks, which I loaded onto each of the players:

  • Pink noise, first with no load, then the same pink noise file with standard Apple earbuds plugged into the unit
  • a 40Hz square wave, with and without the earbuds. The 40Hz square wave is an extreme test, since it asks the output stage to act like a servo amplifier, driving to a full voltage, holding it at that level, then driving back the opposite way.
    This is really a test of the output stage and possibly the power supply, but it's been noted many times that an amplifier is nothing more than a modulated power supply.

    All of the digital audio players do a decent job of reproducing the square wave without a load. With the earbuds plugged in, they generally have difficulty sustaining the voltage, and it collapses back towards zero. Some sustain better than others. One in particular sustains remarkably well and subjectively has noticeably better bass response.

    The five players I tested, in order the quality of their perceived bass performance in listening tests were:

  • iPod Shuffle
  • Zen Micro
  • Dell DJ 20GB
  • 15GB iPod (3rd Generation)
  • iPod Mini

    All but one of these players use single-ended, capacitively coupled output stages. It's an inexpensive and effective way to deliver acceptable, if not superb performance, but the size of the coupling capacitor and the impedance of the headphones have a significant effect on the player's ability to sustain a complex bass tone.

    The screen shots below are just a small portion of the testing I did, but should give you an idea of the differences among players. The spectrum analyzer and oscilloscope are part of the Acoustic Analyzing System 5E, from www.ymec.com.

    I used an M-Audio Transit USB, an external USB sound card, as the audio interface. It has a high-impedance input that doesn't load the circuit under test, and it has no external adjustments for gain--no knob settings to screw up; identical results from test run to test run. It also has better than 100dB signal-to-noise ratio and can sample at 96KHz, sufficient headroom for tests like these.

    This is the Dell DJ20, identical in performance to the current DJ30. Apart from some overshoot, it does a pretty good job of generating an unloaded square wave. It has good subjective bass performance. But unloaded square wave performance doesn't really tell you all that much--unless the player can't form a decent square wave, as one below couldn't.

    This is the Dell DJ20 with the headphones plugged in. You can see how the voltage can't be sustained with the load, but players with curves like this still manage to sound pretty good. If the voltage doesn't sink all the way to zero, the player sounds noticeably better in bass response.

    This is the Dell DJ20 with pink noise. The top line is the response without the headphone load; the bottom line is the response with the headphones plugged in. The load of the headphones has little effect on the upper frequency response, but the drop is noticeable at lower frequencies.

    Above, the 15GB iPod does a near-textbook job of generating the square wave...

    ... and falls down badly when it comes to sustaining it under load. In my testing, players that were dragged down to zero by the load of the earbuds didn't sound as full as the ones that had a little left in in the tank at the end of the cycle.

    My son took the 15GB iPod back to college with him before I could run the pink noise tests. I did, however, record a 1/3 octave sweep test. It doesn't show no/load load. While the iPod is generally well-regarded, bass performance is not stellar. This sweep was run with the headphone load, and you can see the fall-off in the lower octave. The rest of the frequency response curve is flat, however.

    Above is the original iPod Mini (not the new 6GB Mini). It has trouble making a clean square wave or even sustaining it when the player is unloaded.

    Once I plugged in the earbuds, the waveform of the iPod Mini really deteriorated.

    Audiophiles and high-end headphone manufacturers agree that Apple undersized the output capacitors on the Mini, whether for space, cost, or power reasons.

    With the pink noise test, this Player 3 shows a larger variance between the load and no-load lines than any other player in the test. The divergence, as expected, is greatest at low frequencies.

    The Zen Micro does a pretty good job of generating the unloaded square wave, above.

    The Zen Micro's signal sinks when it hits the earphone load, but it doesn't sink to zero. Subjective bass response on this player is pretty good, better than most.

    The Zen Micro shows little divergence under load from its no-load performance. This player did very well in listening tests and is well regarded.

    Above, the iPod Shuffle. The square wave is just about perfect--the overshoot might be heard as a small amount of harmonic distortion, but is immaterial.

    With earbuds, the iPod Shuffle's signal looks darn near identical to the no-load signal. I checked and rechecked this result because I couldn't believe my eyes. The iPod Shuffle sounds great, with a solid low end, and no need for bass boost.
    The reason for this sterling performance is that the left and right channels each have two transistors, one pushing, one pulling, and no capacitor that gets discharged over time.


    The pink noise performance of the iPod Shuffle is, as you might expect, exemplary. The load/no load performance is very close, even at the deepest bass frequencies.
    You might be wondering why these pink noise charts seem to sink down as frequency goes up. The reason is that you're looking at a logarithmic chart, and the intensity of pink nose tapers off as frequency goes up. This is to avoid the problem of white noise, which has the same amount of power at every frequency. That sounds like a good thing, but in fact would mean that fully half of the sonic power would be above 10KHz, and sound just isn't like that in the real world. Pink noise is more representative.

    Update
    Since I wrote the column, Apple introduced the iPod Mini 6GB. I subjected it to some of the same tests as the other players, and as you can see from the screen capture above, Apple has obviously improved the audio amplifier. The 6GB Mini sounds noticeably better than the original Mini.

    The curve gets pulled down to zero with standard Apple 32 ohm earbuds. We could have hoped for more capacity, but it's still better than the original iPod Mini.

    I didn't get a chance to run the load/no load sweep test on the 6GB Mini, but I did run a 1/3 octave sweep with the earbud load. You can seen from the graph that the lowest frequencies are still somewhat deficient, but there's definitely more bass from 30Hz on up.

    In Conclusion
    You can see how much the earphone load affects audio players other than the iPod shuffle. I still haven't reverse-engineered the shuffle design to tell you what Apple did right, but the differences are obvious, both in casual listening and under the testing I've done here.

    Posted by machrone at 08:41 PM | Comments (2)