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Non-linear frequency scales

There are many non-linear frequency scales that approximate the sensitivity of the human ear. For example:

In practice, there is not much to chose from, unless you are interested in auditory model research.

The mel scale is common amongst engineers as it has a simple analytical form:


where f is the frequency in Hz and m is the resulting mel scaled frequency.

For example, this may look like: Filter specifications for a 19 - channel vocoder (Holmes 1980).


Figure 12: The Holmes filter bank

Another reason to use a non-linear frequency analysis is to get around the frequency/time resolution tradeoff. Using a narrow bandwidth at low frequencies enables harmonics to be resolved but gives poor onset information. Using a larger bandwidth at higher frequencies allows for high temporal resolution of bursts, etc.

Speech Vision Robotics group/Tony Robinson