After reading Chris' comments to my post yesterday [comments], I decided to find out what companding is all about.

The purpose of the companding process is to preserve the signal-to-noise ratio of the original audio. If the audio had been transmitted with its full original dynamic range, the SNR would have lowered to roughly 60 dB to 80 dB by the noise introduced by wireless transmission. However, because the dynamic range of the transmitted audio is reduced to only 50 dB, it is nearly unaffected by the transmission noise [Audio-Technica].

This is an interesting process that I was not previously familiar with. However, in addition to the companding process, which is used to supress noise introduced into the signal, there is another type of dynamic range compression used in cellular phones.

Before the companding process, the audio signal is "compressed" to equalize volume levels. The purpose of this type of compression is to keep the volume levels even. I have used this technique extensively, in streaming media, to process audio prior to encoding. I had a hard time finding anything online to explain this technique in detail but I did find a couple of rambling pieces by audio engineers complaining about the abuse of dynamic range compression in commercial CD's [Pro Audio Rx]. 10:34:37 AM    comment []