Pitch & Frequency (was:Re: FS and "AKO Phasing" update)

[media at mail1.nai.net]

>>Hang on a minute, I always thought that perceived pitch is the same as
>>received frequency. Would someone explain why it isn't the case?

It is the case.  The frequency of a wave determines its pitch, as a note is
defined by the frequency of its fundamental.  However, there are also a
number of harmonics whose frequencies have a fixed ratio to this
fundamental.

While both frequency shifters and pitch shifters can change the frequency
of the fundamental, only a pitch shifter attempts to preserve the
realtionship of the harmonics.

>I think it's mostly historical usage. Heterodyning "frequency"
>shifters always shift all input frequencies by the same absolute
>amount and, in so doing, render a harmonic input inharmonic.
>Speed-up/slow-down "pitch" shifters shift in the time domain
>and, therefore, maintain harmonic relationships.
>
>My guess is that, because of the inharmonic output that frequency
>shifters produced, marketing departments wanted to differentiate
>their new harmonic-ratio preseving devices with a word more
>closely associated with music.
>
>Then, of course, I could be wrong.

I believe you are correct.  Pitch shifters are used to change the pitch of
a sound in a "musical" way -- transposing one note to another.

Frequency shifters are used to control feedback in sound reinforcement.
Occaisionally, the kind of wild and crazy guys who read this list use them
to create special effects :)

Has anyone built a digital FS??

>>Pitch Shift is implemented by storing pieces of the waveform and
>>playing them back at a different rate (digitally, using a
>>bucket-brigade delay line, a Hammond flying chorus delay line, with
>>tape, or with the Doppler shift in air) while Frequency Shift is a
>>variation on Ring Modulation.

Right.  What may confuse some folks is that people talk about ring
modulators as multiplying  frequencies.  This may mislead people to believe
that what the output contains is the product of input frequency times the
modulating frequency.  This is not the case.  When you multiply by a
frequency in a ring modulator, you are adding (and subtracting) that amount
of frequency to the input frequency.

Let's look at the chart:

>Number  Original     PS        FS
>
>1       100Hz        100.2Hz   100.2Hz
>2       200Hz        200.4Hz   200.2Hz
>3       300Hz        300.6Hz   300.2Hz
>4       400Hz        400.8Hz   400.2Hz
>...
>10     1000Hz       1002.0Hz  1000.2Hz

So a frequency shifter adds or subtracts a constant value (eg. .2Hz) to the
fundamental and each its harmonics, while a pitch shifter multiplies the
fundamental and each of its harmonics by a constant value (eg. 1.002 or
+.2%)

>>About Lesley: I always thought the doppler effect would really cause
>>a pitch shift, not frequency shift, but I am not sure at all, so I have
>>to think of this again.

Well you have the obvious pitch shift due to doppler effect and the
modulation in volume due to the directivity of the horn (which is slightly
frequency dependent because the absorption coefficient of any material
varies with frequency).  Beyond that, there are nodes and reverberation
from reflections within the cabinet whose relation to the transducers keep
moving, wind noise, the non-linear response of the compression driver
(horn), and the coloration of the microphone.    If that's not silly enough
for you, throw in the centrifugal force on the voice coil :)

PEACE OUT :)
MARK