Thursday, 02 May 2019
What kbps and kHz rate should I record at for CD quality?
Frequently asked question which people can discuss endlessly.
KHz measures the sampling frequency in kilo-hertz – that is it indicated the number of thousands of samples per second which make up the sound file. CD audio is in 16 bit stereo at 44.1 KHz, which means it has 44,100 samples per second, each sample consisting of two 16 bit elements, one for each channel of the stereo.
OTOH kbps is actually a measure of data transfer rate – it means kilo bits per second, i.e. the number of thousands of bits transferred per second. When applied to MP3 files it refers to the rate at which the file would have to transferred for the audio data to be transferred in real time (i.e. for 1 seconds worth of audio to be transferred in 1 second of elapsed time). Essentially this means it is a measure of how much the audio data has been compressed in creating the MP3 files. Uncompressed CD audio data requires a transfer rate of 1,411.2 kpbs (16 x 2 x 44,100), so MP3 data encoded for 128 kbps is compressed by a factor of 11.025.
As to what MP3 encoding rate can approximate to CD quality data to the satisfaction of a listener – well that’s the part people argue about endlessly. It depends on the individual listener, and on the playback equipment and the circumstances. I think it’s fair to say that few people feel that a rate of lower than 128 kbps is adequate. A lot of people find 160 kbps good enough, but some still hear problems and go for higher rates. Also all encoders are not equal, allowing more room for discussion (that is encoder X may produce much better sounding files at 128 kbps than encoder Y).
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