audible hiss...
  • Hello guys, i’m new to Ambika and very impressed by it’s sound possiblities.
    However, I noticed that there is often a audible “hiss” sound when a note is played. In some programs it’s more obvious.
    Is this is normal? Or might there be some hardware issue (like sound distorion, EMC..issue) with my Ambika?

    I have recorded a short clip with factory program A002 A006 A008 playing C4 G4 C5 notes.

  • Yes it’s normal, especially with the SMR4 filter boards.

    It shouldn’t be worse than other vintage analog synths, though – about 70dB lower than the tone emitted by a full amplitude oscillator through an open VCF and VCA.

  • Does the compact nature of the soundboards contribute or is it down to components?

  • LM13700s with darlington buffers, ewww.

  • Thank you Olivier! I do use 6x SMR4 boards:) @pichenettes
    I’m curious… how is the hiss generated exactly? Is it generated by the filter circuitry itself? Or the stepping of filter cut-off control signal (due to bit resolution)? Or from the oscillator?
    it seems the hiss start to emerge when the filter frequency goes above 40. Also I noticed the hiss is not stationary during the entire note on… it sounds as if it’s volume is modulated by some envelop or LFO...

  • The hiss comes from the LM13700.

    With the LM13700 you have two options: either you use the linearization diodes and get a rather “bland” sound; or you do not use the linearization diodes and get a more interesting sound (due to distortion) and work with lower signal levels. Lower signal levels means a lower SNR.

    The filter is a cascade of 4 stages. When you close the filter, the noise from one stage is filtered by the subsequent stages. When the filter is fully open, the noise contribution from one stage is passes through the subsequent stages.