Some of my recordings sound like Tom Waits after a two-day cigarette bender

December 11, 2006 5:34 AM

Crackly, scratchy distortion on the low bass notes on my recorded music: Audiophiles, what's the cause?

Disclaimer, here. I'm a complete noob on all matters audio, but can wing it with a (within reason) technical response, so audiophiles, fire away.

A small but significant chunk of my recorded music, both CDs and mp3s, contains tracks that produce annoying, scratchy distortion on the low notes. The biggest offender: A few cuts on Radiohead's "Amnesiac" album, particularly "Packed Like Sardines," the opening track.

The crackly sounds on this album, and several others, tend to go away when I change the iTunes equalizer to "Treble Booster" from my favored setting, "Bass Booster" (which sounds best over my head phones). So I'm fairly confident that the noise is unrelated to my head phones, CD player, or bugs in iTunes.

I doubt if there's a fix to this issue, apart from changing my equalizer settings, so I'm cool with it for now. I'm more interested in the technical issues. What's the physical source of the low-note scratchiness? Why do producers allow it to infiltrate CDs? (Sometimes it's put there for an old-school analog-y sound, but that's not the case with my albums). Is this a quality control issue, a "let's keep the costs down" issue, or something else?

posted by Gordion Knott to technology (14 comments total)

I've no idea the sources to which you're referring, but the common elements to which your post refers are your player and headphones. It's quite likely your headphones have a problem with their drivers, or are presenting enough of a load to your CD player's amp to cause it to distort. For example, the far higher current demanded by your headphone to reproduce bass notes can cause a borderline female jack in your CD player to not be able to supply full current to the headphones. In the same way, a broken cable in your headphones can be just barely making enough contact to seem to work, yet not be carrying the amperage needed to reproduce bass notes cleanly, especially when the equalizer settings for bass are emphasized. (The human ear being fairly insensitive to low bass, it takes hundreds of times the amount of actual electrical power for bass notes to be reproduced as apparently loud as treble notes intended to be of equal volume.)

For starters, I'd take the source material and the headphones to another computer, and listen carefully to be sure, and if it still sounds broken, try some different headphones. Carefully wiggle the jack and the headphone leads while listening, to see if you can isolate or reproduce similar noises, pinpointing a broken lead wire.
posted by paulsc at 6:14 AM on December 11, 2006

If this was happening with lots of music, regardless of EQ setting, there might be something wrong with your equipment. However, the fact that it's only some music on a particular EQ setting indicates it's nothing to worry about. If an album is mixed bass heavy, adding more bass by using a bassy EQ setting could cause your music to distort as it is played. Therefore, just disable the EQ on music that distorts!

For what it's worth, I also like the iTunes (iPod, in my case) Bass Booster EQ but I still have to turn it off for some heavy albums (Converge's You Fail Me, The Number Twelve Looks Like You, Ed Gein) because I get a distortion similar to the one your describe.
posted by pollystark at 6:49 AM on December 11, 2006

The iTunes equalizer is boosting levels "over" 100%, resulting in clipping. Just lower the preamp setting, or, equivalently, lower all the frequency settings by some amount X so that they're all below zero, but still have the same values relative to each other.
posted by equalpants at 6:58 AM on December 11, 2006

Sounds to me like you are over-driving your speakers/headphones. Especially since you say that your normal setting in iTunes is Bass Booster. This tells me that your current speakers/headphones don't have a bottom-end to your liking and you are trying to compensate...and are driving the little things to distortion.
posted by Thorzdad at 7:21 AM on December 11, 2006

Aside from equalpants' answer (which means you're music will get quieter), the only solution is to get better headphones.
posted by MetaMonkey at 7:51 AM on December 11, 2006

I second equalpants; this sounds like hard clipping.

The songs you're talking about were probably mixed bass-heavy to begin with, without a whole lot of headroom, so when you then boost the bass on them, the result is that there's nowhere to go. A downside to digital audio vs analog is that a too-hot signal starts to sound very ugly when it gets clipped.

You can get an idea of what's going on by clicking on the little right-facing arrow (located to the left of the song title, at the top of the iTunes window) when a song is playing, this switches the display to a meter-ish display broken out by frequency. If any of the bars (particularly those on the extreme left and right) are close to the top, you're probably clipping. However, even if they're not, you might still be clipping somewhere further down in the signal chain.

If turning the preamp gain down (on the EQ window in iTunes) causes the problem to go away, then you can apply a per-song volume correction to the offending tracks; that should fix it.

If it turns out not to be clipping, then you're going to have to start swapping out components and working to isolate the problem on the analog side.
posted by Kadin2048 at 7:57 AM on December 11, 2006

Using the bass boost EQ setting can definitely cause distortion or clipping. Especially with "hot" albums. Unfortunately most of Radiohead's albums are mastered hot. Better headphones isn't going to help—it's the file that's clipping, the speakers are just reproducing it.
posted by mealy-mouthed at 8:20 AM on December 11, 2006

Hmm, I should have given a fuller answer earlier.

As others have said, the likely reason your bass is crackling is because the bass-boosting is causing either digital clipping, or is overloading the headphones' speakers. The reason you are boosting the bass is most likely that you find your headphones' bass response inadequate, so you are attempting to correct this with equalisation.

If it turns out the problem is digital clipping, better headphones would probably help because they would probably give you better bass, meaning you wouldn't feel the need to boost the bass in the equaliser.

If it is the headphones' speakers which cannot handle the levels of bass you are putting through them, better headphones is the solution.

If you get back to us after checking if your bass is clipping in your iTunes meters it'd be handy. Also, what kind of headphones do you have? And also also, do you ever use speakers, and if so does this have the same problem?
posted by MetaMonkey at 9:04 AM on December 11, 2006

Furthermore, it'd be useful to know your setup. Are you playing CD's through your computer? Do you plug your headphones directly into your sound card, or do you have a seperate amplifier, or maybe an all-in-one box?

And just to be clear (re: your question) it isn't a production problem, no modern recording would feature anything like crackly or clippy bass unless its for very specific effect. However, if the problem is digital clipping this may be related to mealy-mouthed's wikipedia link on the loudness war, whereby music has been mixed louder and louder, so that it is already close to clipping when you buy it, leaving no room for simple boosting by your system.
posted by MetaMonkey at 9:18 AM on December 11, 2006

You are little vague on what kind of equipment you're using when the problem occurs. Is it only happening with your home stereo, or with your computer speakers, or what?

It's possible that a cone that reproduces bass in one of your speakers (which would be one of the larger cones) is actually cracked or damaged, or that a connection to that cone is loose, and is being intermittently disconnected by the vibration of the cone itself.

Even if your speaker(s) is/are undamaged, if you want better (louder and cleaner) bass reproduction, definitely look into better headphones and better speakers. It can make a huge difference.

Bass frequencies are some of the trickiest to reproduce, and inexpensive headphones and speakers will tend to distort the low end when pushed to extremes (by loud volume or by a bass boost setting).
posted by Artifice_Eternity at 11:07 AM on December 11, 2006

Something else to look for, if you're listening on prebuilt Windows desktop or notebook, is one of those little "sound enhancer" programs they sometimes include.

Hover over the various icons in your system tray and if anything named "virtual sound" or "sound effects" or the like shows up, kill it or turn it off. A friend's Toshiba laptop had some sort of SRS thingy that mucked his sound up.
posted by cps at 11:39 AM on December 11, 2006

Some explanation of my equipment: the type of headphones I'm using are Sennheiser HD 580s (not top of the line, but okay I suppose), and I've got them hooked into a Boostaroo (tm) audio booster that goes into the headphones port of a Mac Mini. I mostly listen to mp3s stored on my Mac through the 'phones.

Not the ideal setup for quality audio, I know . . .
posted by Gordion Knott at 1:01 PM on December 11, 2006

It seems likely the Boostaroo is your problem (the Sennheiser HD580's should be great, unless broken). It's a cheap signal amplifier designed for cheap headphones, or to split a signal among several pairs of phones. Here's a review saying as much.

Try it without the boostaroo, and see if the problem goes away. If it's too quiet without the boostaroo, you can try digital gain in your eq (which probably won't be too good), or get a better headphone amp. You could also find an old all-in-one or cheap seperate amp to connect to the mac, both would probably be way better than the boostaroo.

Let us know how the relevant songs sound without the boostaroo, and with and without bass boosting in iTunes.
posted by MetaMonkey at 2:27 PM on December 11, 2006

I tested the setup without the Boostaroo, and nothing's changed.

However . . .

I disabled the Preamp in the iTunes equalizer, and the clipping diminished, without much of a reduction in sound quality (to my uneducated ears).

Wonder if this is the correct route to proceed?
posted by Gordion Knott at 3:15 PM on December 11, 2006