In my previous post, it seems I’ve made some serious errors when discussing the technicalities of music recording, both digital and vinyl. This is not my area of expertise and I apparently did not do nearly enough research. Thanks to Gregor Robinson and Jonathan Griffitts for correcting me. Here are Gregor Robinson’s and Jonathan Griffitts’ corrections verbatum. Thanks to both of you.

Gregor Robinson said:

There is actually a big difference between lossy formats and lossless digital audio formats (which may be in fact compressed; see FLAC). It’s not just that the sample rate is lower. Lossy compression makes use of interpolation and other tricks to approximate the original lossless digital signal, whereas lossless compression makes use of inherent redundancy of the digital information. Some signals are more redundant than others (http://en.wikipedia.org/wiki/Information_theory).

The MP3 codec, for instance, is a lossy format that relies on a model of the human auditory system to estimate portions of the waveform that are difficult for the human ear to notice. The MP3 encoding algorithm identifies the presence of frequencies that are probably “masked” by the presence of others — and just plucks them out of the file like they never existed. It turns out that formulating accurate models of psychoacoustics is difficult, and people vary, which makes this process imperfect. So there’s no surprise that many people hear significant difference with such codecs. The difference is exaggerated at low sample rates.

As an experiment, try converting a WAV or other lossless format into pairs of files of similar sampling sampling rates (be sure to disable VBR — how to do this depends on your encoder). Make one an MP3 and the other a WAV. See what happens when you vary the bitrate. Listen to the sea-alien sounds that start to happen when you start cranking down the MP3 bitrate.

Jonathan Griffitts Said:

This information is not actually correct: “Sound is recorded on a vinyl record by copying the shape of the sound wave onto a groove on the record. The stronger the pressure, the deeper the groove.”

The sound information is actually recorded by motion on the other axis, wiggling the groove to the left and right (that is, radial motion relative to the center of the record). The groove actually looks like a tiny graph of the sound waveform, big enough to be seen with minimal magnification (well known to oldsters like me who have handled a lot of vinyl records). On monaural records that’s all there is, but on stereo recordings the depth of the groove actually records stereo information, specifically it represents the difference between the two channels.

I do a lot of work involving signal processing and the relationship between sampling rates and signal bandwidth. Therefore I’m really tempted to launch into a nerdy clarification of the relationship between sampling rate and signal bandwidth, and just what is meant by “resolution”, but I’ll spare you.

I apologize to everyone I misinformed earlier this week.  I will do my research more thoroughly the next time I explore a subject I don’t know well. Thanks for reading, everyone.