Filter For Audio Measurements

Posted on Mar 31, 2013

The purpose is supposedly to account for the fact that human hearing is less sensitive at low and high frequencies than in the upper midrange, and that this variation is dependent upon the sound intensity (SPL). The Fletcher-Munson curve (as it is commonly known, and reproduced below) shows the variation, and it is clear that any loss of sensitivity is highly dependent upon the actual SPL. The idea that a single filter can represent this at all levels is clearly wrong, but it is a standard nonetheless. (Interestingly, being wrong has never stopped a standard from being imposed, and this is probably truer in the audio industry than almost any other I can think of.)

Filter For Audio Measurements
Click here to download the full size of the above Circuit.

The premise behind all this is that as the SPL is reduced, our ability to detect low or high frequency noise is reduced, so measurements should reflect this phenomenon. While it is undeniable that the chart above represents reality in terms of human heari

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