MP3
Compression efficiency of encoders is typically defined by the bit rate, because compression ratio depends on the bit depth and sampling rate of the input signal. Nevertheless, compression ratios are often published. They may use the Compact Disc (CD) parameters as references (44.1 kHz, 2 channels at 16 bits per channel or 2x16 bit), or sometimes the Digital Audio Tape (DAT) SP parameters (48 kHz, 2x16 bit). Compression ratios with this latter reference are higher, which demonstrates the problem with use of the term compression ratio for lossy encoders.
What can CD parameters be used as references for?
compression ratios
Nevertheless, compression ratios are often published.
references