[Fpga-synth] Signals and Sample Rates

[Scott Gravenhorst]

I am trying to understand how to deal with signals and sample rates.

For example, when a limit is given, such as for a digital state variable filter being 1/6 of the sample rate, higher frequencies causing instability, I think that this means a sine wave at 1/6 the sample rate.  But most of our synth signals are not sinewaves and thus can have frequency components much higher than the fundamental.  

How does one deal with the transients in sawtooth or rectangular waves?  

Is it "OK" to use such a filter because the energy in the highest harmonics tends to be diminished?  

I like the sound I get out of a digital SVF, but that's in a synth with a sample rate of 1 MHz.  Seems to be enough headroom there.  However, I'm working on a synth that currently has a sample rate of 125KHz.  That sets the limit much lower at 20.833 KHz.  Is that my magic number (being just above what most of us can hear) ?  I.e., is 125 KHz too low?

What sorts of things will I need to look for to judge the quality of my SVF at that sample rate?

-- ScottG

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-- Scott Gravenhorst
-- GateMan-III - FPGA Based Monophonic MIDI Synthesizer with SVF
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