The following discussion took place on the Analogue Heaven
mailing list around 2002-08-28. Keywords: SIEL Mono, SIEL Cruise.

André Majorel :

  I'd like to know if your Cruise has the same problem as my Mono.
  Namely, on the sawtooth oscillator, there is a parasitic sound
  that sounds like a second sawtooth but exactly four octaves
  higher. This happens only on the sawtooth ; square and pulse
  sound fine. The parasitic sound is not loud but since it's high
  pitched, it's quite audible.

    http://www.teaser.fr/~amajorel/mono/sawtooth/monosaw.wav - Low C
    http://www.teaser.fr/~amajorel/mono/sawtooth/monosaw2.wav - C to A

  On the above samples, the parasitic sound is very visible ; a
  sawtooth-ish wave whose period is 1/16th of the fundamental is
  riding on the back of the main sawtooth.

  It's been that way for as long as I remember. Any idea whether
  this is due to poor adjustement, or inherent to the design ?

Sander Meyer :

  Yes I have the same problem.
  The following I posted to AH 3 years ago beat I didn't got an
  answer then:

  > The Cruise can make real nice bass sounds, but when you listen to
  > it trough a headphone, I hear a sort of second tone. For example
  > use the free mode above the bass preset and turn on the down the
  > resonance and move the cutoff a .bit up. You will hear a nice
  > bass sound, but you hear a higher sound as well.

  Here is an example of mine:
  http://www.smeyer.cistron.nl/cruise.mp3

  Should there be a fix for it?

  I also wondered if it isn't possible to mod the Cruise so that
  poly parameters (filter, chorus) is available for all poly sounds?
  And cv/gate ins for the mono part

Tony Allgood :

  I think this is probably due to the fact that the sawtooth is
  not a real sawtooth at all, but a mix of square waves at
  different octaves added together to give an approximate
  sawtooth. It should be possible to adjust the levels of these to
  give a very good sawtooth, but it will never that perfect.

  This is sometimes to a great advantage. The bass guitar preset
  on the SH2000 has a sawtooth feeding the filter. But the
  sawtooth is highly stepped due to its creation with square
  waves. This gives a nice edge to the sound and its very very
  close to the real thing. This is not easily done with ordinary
  saw VCOs.