Masking

masking is based on masking properties of the human ear. In contrast: When you look at the sun and if a bird passes ahead, you do not see it because of the too predominant light of the sun. In audio, it is similar. During strong sounds, you do not hear the weakest sounds. Take as an example a piece of organ: When the organist does not play, you hear the breath in the piping, and when he plays, you no longer hear it because it is masked. Different types of psychoacoustic masking exist and are exploited in most coding systems.

Masking properties

• TMN tone masking noise
• NMT noise masking tone
• TMT tone masking tone

Simultaneous masking

Simultaneous masking is a frequency domain phenomenon, where a low-level signal (noise) commonly referred to as the maskee can be made inaudible by the presenence of a stronger singal masker (i.e high amplitude pure tone masking a noise). Several of the masking properties listed above are deployed in most coding systems (psychoacoustics models, etc), these vary depending upon the characteristics of the signal. The masking threshold for each varies depending upon a number of characteristics, which are limited to the SPL and frequency of the masker. In practice high frequency noises are more easily masked.

Temporal masking

Temporal masking is a time domain phenomona by witch masking can be exploited before and after a signal, hence pre-masking and post-masking. The onset of pre-masking is relatively short and doesn't last upwards of 20 msec. In contrast to that of post-masking, which can last upwards of 50-200 msec after the signal that is being masked.

Additional reading

• Masking Effects this applet demonstrates the effects of masking in perceptual coding.
• Human Auditory Masking differences between auditory perception in masking.