Audiophile Question: Total Harmonic Distortion

Back in the days of component stereo, people were crazy to get gear with lower THD-audiophiles were willing to pay big $$ to get ).1% lower THD. My question: today, most people seem happy with compressed audio. When you compress an audio track (MPEG or similar), do you wind up introducing distortion? True, most peoplem cannot detect it unless its up to about 2%, but are we regressing in audio technology?

I don’t know that the effects of compression are described using the word “distortion.” Distortion is when the circuit can’t handle the signal and clips off what it can’t handle. Compression substitutes data with formulas that take up less space and “more or less” represent the data mathematically.

That compressed signal is does not have fidelity to the original signal, but the problem is not distortion.

To answer your question, yes, some compression algorithms, played back on earbuds, sound pretty darn bad.

As WordMan said, THD and compression aren’t really measurements of the same thing at all. But! both of them have to do with the accuracy of the sound reproduction.

THD is a quality of an audio circuit, whether it’s an amp or a speaker, and it only relates to how closely it reproduces its input. Even then, even-order harmonics can be pleasant to human hearing, and some amount of it is desirable.

Compression, in how the term applies to music storage, relates to how the data is sliced and diced for easy storage. Some methods of slicing and dicing don’t lose any fidelity, but they use more space. Others sacrifice quality for quantity, most even allow you to store a high quality copy that only loses the wavelengths that humans aren’t likely to notice. The ones that lose some of the signal increase distortion. Depending on what you’re used to, and what encoding process was used, you might even find that pleasant.

As to whether we’re regressing in audio tech, I dunno. I’ve heard people claim that Norman Greenbaum’s “Spirit in the Sky” didn’t sound right unless it was over AM radio, in mono. Once you’ve got the windows down, who cares?

This is a bit of a generalization. Some audiophiles pay huge bucks for things like single-ended triode amplifiers or zero-feedback class-A transistor amps, both of which have terrible THD specifications (and terrible efficiency). Others do goofy things to DACs (like using current-output DACs without a buffer amp, in order to “reduce the active components in the signal chain”) which also drive up distortion. Others do strive for lowest THD. Or noise floor. Or transient intermodulation distortion. Or whatever.

Regarding compression, there are actually two types of compression. One is data compression, which is reducing the size of the audio data file. this can be done losslessly (i.e., no information is lost and the data decompresses to the original) - FLAC and ALAC are examples of lossless compression. There is zero impact on sound quality. More common is lossy compression (most commonly mp3) which uses quite advanced algorithms (based on psychoacoustics) to remove information from the data in such a way as to minimize the audible effect. Depending on the actual compression algorithm and compression settings, audio quality can range from clearly degraded to indistinguishable from the original. I personally use FLAC (lossless) compression on anything I listen to over my home network (some of which feeds some pretty high-end equipment) and pretty highly compressed mp3 for listening to in the car or on earbuds (where the environment is lousy anyway).

The other type of compression is audio (or dynamic range) compression, which is basically selectively increasing the volume of the quieter parts of the music so there is less difference between loud and the soft. This makes the music sound louder, and most people perceive louder to sound better - but at the cost of (IMHO) an inferior listening experience. Audio compression also helps in noisy environments where most people seem to listen to music these days.

As to is audio tech regressing? I don’t think so. Even pretty compressed mp3 sounds better (IMHO) than vinyl (the signal-to-noise ratio of vinyl is pretty low), to say nothing of cassettes and (gulp) 8-tracks. As for high-end (audiophile, if you must) there are still a lot of companies out there trying to advance the state-of-the-art in audio equipment. You just can’t buy their products at Best Buy.

I have to disagree. I’m no “vinyl vinyl uber alles” types, but “pretty compressed” mp3 (192 and lower) starts showing compression effects such as ghosting, flanging, and frequency loss that are very noticeable even at my age. They only significant problems I have with vinyl is dirt noise and pops and scratches.

And as for cassettes, in general they can be bad, but I used to have a Yamaha that had 20-23K response and a 95db SN ratio. When I recorded CDs onto cassette, i could hear the difference in background when the CD stopped - the cassette was quieter than the CD ambient background noise!

Obligatory audiophile digital pr0n.
You’ll want a set of these to play it…

I have a fairly well-trained ear for music (I took piano lessons for about a decade and play several other instruments). For a lot of types of music, I can’t hear the distortion in an mp3. But there are some things, especially piano and acoustic guitar sounds, that get mangled horribly by mp3 compression. Some of it I almost can’t stand to listen to.

There are lossless compression algorithms out there, but mp3 isn’t one of them. If you want better sound though, there are better formats that you can use that don’t ruin your music like an mp3 does.

A number of year ago I was designing an audio CODEC chip. A coworker (who I believe had done his PhD research in psychoacoustics-based compression) offered to teach me how to identify compression artifacts in mp3 playback. I declined, because I figured that once I knew how to identify artifacts I would hear them all the time and it would drive me crazy.

That’s why I never point out to people* that TV and movies almost always wet the streets before filming, even on a sunny day, because dry asphalt looks bad. And once you notice it, you’ll notice it all the time.

*Well, except for telling you all just now…

And not the constant shhhh noise the entire time and complete lack of bass? I bet you could cover up a lot of MP3 artifacts with that.

Not that I hear anything at 192 kbps. 128? Sure. But not 192, unless you count the top frequencies being cut as you should in a properly encoded MP3.

Complete lack of bass? You need a better turntable or better records. It doesn’t require anything special, an old Realistic will do if you’re in a pinch. Vinyl has plenty of bass, you just can’t pan it hard left or right when you’re mixing for it.

You can get so much bass that the needle can jump out the groove.

Maybe he’s plugging the turntable into the wrong jack? You need the biased turntable input or the sound is all tinny.