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April 8, 2010

Filed under: music»recording»mp3

Bitrot

Digital files don't wear out, right? This is one of the big advantages of the medium, particularly in studio situations: people love the warmth of tape, but it's fragile and it loses a tiny bit of fidelity every time you play it, much less when you make a copy. If you read a lot of studio how-to articles (a guilty pleasure of mine), a common theme is the engineer who records on tape for the sound, then immediately dumps it into Pro Tools for actual editing and mixing. And of course you can make a perfect copy of a digital file, where as there's no such thing in analog.

With one exception: back when DRM'd music sales were the norm, the typical way to remove that DRM was to burn the file to a CD and re-rip to MP3 format. This was seen as kind of a kludge, because the process involves conversion to a lossless .WAV format and then back into lossy pyschoacoustic compression. In theory, every time this happens, the latter step means a loss of information, and thus fidelity.

But how much of a loss? I started wondering this when I went to make a CD for a fellow dance student from some MP3 files I'd gotten from More Than A Stance. I didn't know how he planned to play them or how tech-savvy he was, so audio CDs seemed like a better choice than audio files on a data CD. But if he decided to rip the CDs back, how bad would the quality hit be? I decided to find out.

Using some shell scripting (first PowerShell, then old-fashioned batch files--never use a computer without at least one scripting option, kids), I sent a couple of MP3 files through a conversion roundtrip a few hundred times. My choices were "Beam Katana Chronicles" from the No More Heroes soundtrack and a remix of the Jackson Five's "Life of the Party" from DJ D.L.'s Soul Movement II, picking these particular tracks for a few reasons:

  • Both tracks are relatively close to the real-world case I was trying to figure out, with the latter being an actual dance track.
  • Both were layered compositions, with plenty of detail to lose during conversion.
  • Both included strong percussion tracks with plenty of hi-hat and snare--the kinds of high-frequency transient noises that easily smear and blur under psychoacoustic compression.
I used LAME to do the decoding and encoding at a 256kbps bitrate. On the first test, I actually ran the file out to a separate .wav and back. The second time, I figured out how to pipe the stdout from one LAME instance to the stdin of a second, and just bounced it between two MP3 files, which was much faster.

The results were surprising. Here's a table with some samples (caution: may be loud), which I'll summarize below.

iterations trackaudio
original No More Heroes
DJ D.L.
50 No More Heroes
DJ D.L.
100 No More Heroes
DJ D.L.
500 No More Heroes
DJ D.L.
At under 10 iterations, I can't tell a difference between the two files. At 30-50, it's subtle--there's a little bit of swirliness around the high end, and the transients are a little blurry, but nothing more than you'd expect from, say, a turntable. It's not until you hit 100 iterations--that's 100 times going from an MP3 file to a WAV and back--that it starts to become noticeable. At that point, there's some definite artifacting, and you can start to hear a little bit of pumping in the volume after each peak. Even still, it's not much beyond the extremes of dynamic compression that have emerged from the loudness wars, and if you snuck it into my playlist I wouldn't guarantee that I'd pick it out. Once you get beyond 100, it becomes more obvious that something's broken. By 500, there's some real glitchiness going on when the track hits full volume--surprisingly, much more in the NMH track than the J5, although the latter also has its "underwater washing machine" moments.

There are a few holes in my experiment that would be interesting to test:

  • I used a symmetrical encoding and decoding process, with the same codec feeding into itself. It would be interesting to see how a mix of two or more encoders would change these results. It's likely that this would accelerate the decay rate, but would it be enough to overcome the sizeable margin in this test?
  • Likewise, this was a test of high-bitrate encoding--simply because that's the scenario where most people would realistically encounter. I'm guessing the minimum bitrate for most people is 192kbps, and anything you buy these days is usually higher. But yes, at lower bitrates I'm guessing this is dramatically more detrimental.
  • Finally, this is a test of MP3. I like MP3, and I think the folks behind LAME have done about as good a job with it as they could, but it is a last-generation compression format. It'd be interesting to see how OGG, AAC, or WMA could stack up against it.

Still, I have to admit this is far better performance than I expected going in, and I was cheering for LAME to begin with. I think we can safely reach the conclusion that for limited, real-world cases of digital dubbing, there's no serious impact on sound quality that wasn't already lost in the first MP3 encoding. Burn and rip away!

June 27, 2008

Filed under: music»recording»mp3

Thumbs Up

If you love the sound of kalimba as much as I do, you may enjoy the pad I created for CQ's upcoming DTV Transition explainer:


MP3 download

Best soundtrack instrument ever. It's just exotic enough to add interest, but not so strange that it distracts from the video. If I had a set of gamelan samples to mix with it, I'd be a happy man.

January 8, 2007

Filed under: music»recording»mp3

Mastermind

A final version (by which I mean that the arrangement is solid and the quality is good enough for the web) of "Mastermind" is now available at Four String Riot. Obviously the little gimmick samples are not technically kosher with my manifesto, but I couldn't resist considering the subject matter.

I did manage to resist using the Digitech Whammy pedal I picked up this weekend, but it is probably the coolest pedal I've ever owned. When the Gib Cima Experience played "Werewolves of London" on Saturday, I kicked in the octave up mode to do the guitar solo, and with a little distortion it sounded just about perfect, including double stops. I may have to record it as a sketchpad. On triple stops or more complicated chord voicings, it still throws up all over the sonic spectrum, but overall it's certainly the best pitch shifter available short of a $1,500 Lexicon MPX-G2 or an Eventide harmonizer. The Whammy's octave harmonize function also does a nice 8-string bass imitation, and I've been playing Pearl Jam's "Jeremy" every time I turn it on.

November 25, 2006

Filed under: music»recording»mp3

Four String Refresh, Part 2

The process of re-recording old songs continues, with overhauled versions of "Lazy Sunday Eyes" and "My Foundation," as well as yet another rendition of "Voodoo Funk." Here's a few thoughts on recording these:

  • I finally figured out why I have so much trouble getting good volume out of my recordings. It's because the bass has such a huge dynamic range the way I play it--at any give time, I could be plucking, strumming, slapping, or literally pounding on the strings. Because I always wanted to avoid the nasty popping that results from overdriving a digital input, I was setting the preamp level according to my highest peak level--in this case, percussive slaps. Since my amp overdrives gently, I hadn't realized how much louder those peaks actually are compared to the rest of my signal. By setting them as the highest, everything else was recorded far too soft. The ultimate solution would be to record the amp itself, but my cabinet isn't in a great acoustic location, and I don't really want to mic my practice amp. After that, preferably I'd add a compressor before the interface, but I don't own a hardware compressor. Instead, I added a carefully set software compressor to the track to limit the pops but boost the gain on everything else. This raises the noise floor a lot, but it's good enough for now.
  • I've also switched to an M-Audio Firewire Solo interface, for a couple of reasons. One is that my Tascam US-122 was obtrusively noisy when using phantom power, which I need for my condenser mikes, and I was having to run them through a mixer. The Solo is externally-powered, so I can eliminate the mixer from my signal chain. Also, using IEEE 1394 instead of USB lowered my signal latency from 45ms to 6ms, making it possible to effectively monitor myself and (hopefully) cleaning up my timing a little. Neither of these were dealbreaking problems, but it's nice to have them addressed, and the Solo isn't that expensive.
  • The software pedalboard experiment is pretty much over. Although it was interesting and I still think there's a lot of power there, I was never entirely happy with the results. I've gone back to my MXR M-80 preamp, DOD Envelope, and Line 6 looper, and I'm just running the MDA Combo plugin to tame the harsh treble and boomy low-end. It's nice to have knobs to play with again.

Hear the results, as always, at the Four String Riot. Next up is to finalize/record "Mastermind," and then start writing again.

November 19, 2006

Filed under: music»recording»mp3

Four String Refresh

There are new versions of "Voodoo Funk" and "We Used To Be Friends" up on the pretentious solo project, as well as the the hateful Myspace. With that said, if you were going to listen to them right away (crickets chirp, tumbleweed, the sound of echoes in a large empty space) you might wait until tonight around 8pm EST--they still need some tuning, and makeup gain (the Tascam US122 has many virtues, but hot input is not one of them). The goal of redoing these songs was that the previous recordings were pretty distorted and sometimes had boxy vocal sound.

Next up are my really old recordings, and then I need to put together three more songs or so before I go out and humiliate myself trying to gig for real again.

October 1, 2006

Filed under: music»recording»mp3

Strange Chemistry

Last seen in Sketchpad #7, I've completed a sufficiently final version of Strange Chemistry, now available over at FourStringRiot.com. It replaces My Foundation until I get that recorded again--the previous version was tracked before I had a half-decent preamp and using Audacity, so the quality was pretty low.

As a test for the virtual recording rig, I'm really happy with Strange Chemistry. I hardly had to touch the levels on the different loops at all, so I could devote more time to making the vocals satisfactory. I recorded the song in a couple of passes in Ableton, tracking the distorted parts on the second pass so that a mistake in the solo wouldn't ruin the whole song. Then I pulled it into Cubase for mastering and fades. My "mastering" process basically just consists of using the MDA Stereo Sim on the final mix--since everything I do is basically mono, I need a little extra separation and MDA Stereo somehow creates the illusion of a big soundfield.

Before I recorded this, I put new strings on the bass, and you can really hear the difference. I love the way the chords ring out--they're very rich and percussive, more like bells than guitar. Whereas the sketchpad version was almost all distortion, I use very little of that channel here. Despite that, I think it's actually more sinister-sounding, especially toward the end when the bass chords begin to slide around each other.

December 5, 2005

Filed under: music»recording»mp3

More songs for the ever-growing army of the undead

There are three new recordings now up at Four String Riot. One of them is just a cleaner version of Voodoo Funk now that I have a USB preamp instead of a laptop soundcard for input. The other two are more interesting.

First is a new original, titled Lazy Sunday Eyes. I tried to get an Elliot Smith-style chorus effect going on the vocals, because I thought it would sound really good lo-fi, but Audacity has basically no facilities for that kind of thing. It's a pretty good song anyway, I think. There are some glaring mistakes left in it, but if I aimed for perfection I'd never get anything online. Belle said she couldn't really hear them anyway.

Also I've added a cover of the Dandy Warhol's We Used To Be Friends, which you may be more familiar with as the Veronica Mars theme song. I think this one worked out very well, and features obnoxious overdubs of my falsetto. I feel a little guilty about that, but note that otherwise all of the new songs continue to follow the basic manifesto for my pretentious solo project: no samples, no drum machines, and no prerecorded backup tracks. Of all the songs I do, We Used To Be Friends probably requires the most footwork for toggling the loop and distortion at the correct times. It's a lot of fun live.

I don't know when I'll be getting more "proper" gigs, because that's a process that requires a lot of work, but with three originals and two hours worth of covers under my belt, it's possible that I could do it fairly soon. As always, it'll be posted here if it happens. In the meantime, I continue to play at Stacy's Coffee Shop on Wednesdays, so feel free to drop in.

September 9, 2005

Filed under: music»recording»mp3

My Foundation


From world-famous Four String Riot Studios...

There's a new original up at Four String Riot. I played this one out at Stacy's this week, and it seemed to go over well. Note for equipment nerds: it uses the Play Once function of the DL-4, which I hope to exploit more as I become more familiar with it.

Also note that I'm not really happy with the recording quality on any of these, which I think comes from recording into a laptop soundcard. The vocals are flattened, and no matter what I do there's a lot of top-end distortion. It makes it really hard to care about fixing the little mistakes that I've left in, when I know it's still going to sound like a 4-track. Swapping the mixer or the mixing software doesn't seem to change anything. This winter I'm going to try to grab one of these TonePort things from Line6 and see if a good USB preamp will solve the problem.

July 28, 2005

Filed under: music»recording»mp3

Voodoo Funk

New original, half-finished.

June 12, 2005

Filed under: music»recording»mp3

A Tiny Monkey Might Work

Does anyone else have this problem? At home, I have a collection of (ahem) illicit music files, some of which are duplicates that I either own or could obtain through fair use, some of which are "research for covers" (justification rocks!). In order to get them to some level of consistent volume, I'm forced to run a pretty heavy compression plugin through my mp3 software. This morning, though, I threw a bunch of new songs onto the iPaq for the Metro ride, and realized yet again that controlling the volume between the Pillows and the Pixies, for example, is just enough of a distraction to pull me completely out of the groove.

I recognize that we don't necessarily want to hand people more ways to mess up their music (don't get me started on equalizer abuse), but are mp3 rippers this inconsistent? Or is this another indication of increasing compression and degraded dynamics in music as time goes by?

Perhaps I need to switch to a more sophisticated Win CE music player. The problem, as I see it, is that the free ones are typical open-source mid-completion, and Microsoft is reserving WMP10 for native devices only--no upgrade available. If only I could find a display model with what I want and Bluetooth installed...

Title via the Monkey Explains It All guide to guitar effects.

Future - Present - Past