I hope this is the most appropriate SE site to ask a question about psychoacoustics.

I don't quite understand critical bands. As far as I know, if two pure tones which frequencies are inside the same critical band are heard, a single tone is perceived. But what would be that tone's frequency?

According to the classical rule of thumb, the bandwidth would be the following:

  • 100 Hz if f<500 Hz
  • 20% of the tone frequency if f>500 Hz

But I really don't know how to apply this. If I have two tones with f1=800Hz and f2=950 Hz, what would be perceived?

Would the critical band be 800-0.2*800=640 Hz to 800+0.2*800=960 Hz and therefore a single tone would be perceived? Or is 0.2*800=160 the real bandwidth (so the band would be from 720 to 880 Hz)? And, if a single tone is perceived, what frequency would it be?

Thank you in advance.


I'm not an expert in psychoacoustics, but in trying out examples such as an 800Hz tone and another (which I varied from 802Hz to 1khz) they were all distinguishable instantly, with no effort. At very close frequencies (ie 0 to about 2 Hz difference) beats were the major audible component, but above that, two pure tones are heard.

The only combinations which caused more interesting results were when one tone was a harmonic of the other - it was possible to 'lose' one in the other tone...


I have been lucky enough to find a whole chapter about critical bands and masking in An Introduction to the Psychology of Hearing by Brian C.J. Moore in college library. The phenomenon I asked about in my question seems to be just one of the many aspects of critical bands. In fact, this is a way to experimentally find out the critical bandwith for each frequency.

Given two complex periodic sounds containing 12 sinusoidal components (partials), which are:

  1. fundamental frequency f0 and its harmonics: f2 = 2 ⋅ f0, f3 = 3 ⋅ f0, ..., f11 = 11 ⋅ f0.
  2. fundamental frequency f0 and out-of-tune harmonics (i.e. not multiples of the fundamental frequency).

Subjects were requested to listen the following pure tones:

  • a tone whose frequency was contained in the previously heard complex sound.
  • a tone whose frequency was half-way between two of the harmonics contained in the previously heard complex sound (e.g. 3/2 ⋅ f0)

Assuming that a partial is only heard when its nearest neighbour is at least a bandwidth away, the stated results for the bandwidth were found:

  • 100 Hz if f < 500 Hz
  • 20% of the tone frequency if f > 500 Hz

The bold sentence being the one that really answers my question.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy