[sdiy] frequency shifters...

[Andre Majorel]

On 2002-07-20 21:03 -0400, Nihiliste9 at aol.com wrote:

>  Hi all. I was wondering if frequency modulation was the same as
>  a frequency shifter.

Not at all. Frequency modulation of a sawtooth gives another
sawtooth, higher pitched. Frequency shifting of a sawtooth gives
Something Completely Different.

As you surely know, all waveforms are equivalent to a sum of sines
whose frequencies are whole multiples of the frequency of the
waveform. Those sines are the partials.

Take a 100 Hz sawtooth : the partials are 100 Hz, 200 Hz, 300 Hz,
400 Hz, etc :

  ^
 a|         |
  |         |         |
  |         |         |         |
  |_________|_________|_________|_________|_______ f
           100       200       300       400
           1.0x      2.0x      3.0x      4.0x

If you modulate it so that the fundamental is raised by, say, 28
Hz, all partials have their frequency multiplied by 1.28 : 128 Hz,
256 Hz, 384 Hz, 512 Hz. The frequencies of the partials are still
whole multiples of the fundamental :

  ^
 a|            |
  |            |            |
  |            |            |           |
  |_________ __|____________|___________|____________|____ f
              128          256         384          512
              1.0x         2.0x        3.0x         4.0x

On the contrary, if you *frequency shift* it so that the
fundamental is raised by 28 Hz, all partials are shifted 28 Hz up;
128 Hz, 228 Hz, 328 Hz, 428 Hz. The partials are now inharmonic :

  ^
 a|            |
  |            |         |
  |            |         |         |
  |____________|_________|_________|_________|_______ f
              128       228       328       428
              1.0x     1.78x     2.56x     3.34x

The result of frequency shifting is often metallic-like sounds.

-- 
André Majorel <amajorel at teaser.fr>
http://www.teaser.fr/~amajorel/