Ladefoged – Chapter 6

[Simon]

Hearing

[Simon V]

On p. 83 Ladefoged concludes that “[a]s the loudness of a sound depends on the rms. amplitude and not on the peak amplitude, the first sound is louder than the second.” (emphasis added)
Comparing this with Fig. 6.2 on p. 82, the second sound should be louder, I think? Is this a typo?

[Siqi S]

On page 76, the author mentions that it is possbile there is no component with a frequency which is the same as the frequency of repetition of the complex wave.

Then He uses an example of component frequencies 1800Hz, 2000Hz and 2200Hz, and the complex wave frequency of 200Hz. This confuses me a lot. Is this a general case for harmonics? (i.e. the greatest common divisor of the component frequencies is the frequency of the complex wave?) or just a special case for harmonics here? (i.e. this 200Hz complex wave happens to have components with frequency 1800 2000 and 2200Hz) Thank you

[Simon]

The signal in Ladefoged Fig 6.2 could be generated by passing an impulse train with a fundamental frequency of 200 Hz through a filter which only passes through frequencies in the range 1 800 Hz to 2 200 Hz. For example, a filter with a single resonance at 2 000 Hz and a narrow bandwidth.

The harmonics in the filtered signal are still at integer multiples of the fundamental. The fundamental frequency of the filtered signal is still 200 Hz even though there is no harmonic at that frequency.

The filter cannot change the fundamental frequency. It can only modify the spectral envelope = it can only change the amplitudes of harmonics, not their frequencies.

One interesting consequence of this is that we perceive such signals as having a pitch equal to their fundamental frequency, even if there is no energy at that frequency. Our perception of pitch is based not simply on identifying the fundamental, but on the harmonic structure.

[Siqi S]

That’s very clear. Thank you!

[Author]

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