Perceptual codecs spend bits only on audible components, discarding masked ones

Evidence

Using some form of simultaneous masking model masking curves, which are different for tonal and non-tonal sounds, a signal to mask­ ing ratio (SMR) is calculated and the bits allocated such that components that need a high SMR are given more bits than those that have a lower SMR. For components that have a negative SMR no bits are allocated because these components are masked and therefore need not be transmit­ ted. The amount of bits that can be allocated depends on the desired bit rate. Also, the process interacts with itself so this process usually is inside some form of optimization loop that minimizes the total perceptual error. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2675

Categorization

• DEFINE: Introduces signal-to-masking ratio (SMR) as the metric governing bit allocation in perceptual audio coding.
• CANDY: Neat hook: your music files simply never encode the sounds you can’t hear.