The correct answer is option 4. The compression efficiency of encoders is typically defined by the bit rate because the compression ratio depends on the bit depth and sampling rate of the input signal. They may use compact Disc parameters as references (44. 1 kHz,2 channels at 16 bits per channel or 2×16 bit) or sometimes the Digital Audio Tape SP parameters (48kHz, 2*16 bit)2 channels of 16-bit audio at 44. 1 KHZ=2×16×44100=1411200 bits/sec=172 k byte/seccompression ratio =172/16=10. 75:1=11:1 0r 10:1? Hence the correct answer is 10:1.