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Masking threshold
The masking threshold is the sound pressure level of a sound needed to make the sound audible in the presence of another noise called a "masker". This threshold depends upon the frequency, the type of masker, and the kind of sound being masked. The effect is strongest between two sounds close in frequency.
In the context of audio transmission, there are some advantages to being unable to perceive a sound. In audio encoding for example, better compression can be achieved by omitting the inaudible tones. This requires fewer bits to encode the sound, and reduces the size of the final file.
== Applications in audio compression ==
It is uncommon to work with only one tone. Most sounds are composed of multiple tones. There can be many possible maskers at the same frequency. In this situation, it would be necessary to compute the ''global masking threshold'' using a high resolution Fast Fourier transform via 512 or 1024 points to determine the frequencies that comprise the sound. Because there are bandwidths that humans are not able to hear, it is necessary to know the signal level, masker type, and the frequency band before computing the individual thresholds. To avoid having the masking threshold under the threshold in quiet, one adds the last one to the computation of partial thresholds. This allows computation of the signal-to-mask ratio (SMR).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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