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Filter for on-board Teensy 3.6 DACs
Does anyone have any advice/suggestions on suitable filters for the on-board DAC?
I'm drawing up a board to help me play with the Teensy and a filter on the audio sounds like a good idea.
I suppose you are talking about hardware filters.
Anyway, it depends on the kind of filter you want to implement. Is it a low pass only? And I would suggest using a bandpass filter on the outputs, to cut away spurious low-frequency 1/f noise and every sampling frequency harmonics. In an ideal world you would cut above 22.05 KHz but in reality you might want to start cutting around 15-18 KHz.
I've been looking into filters like these in the last weeks and in my opinion a good topology for an output filter would be a 2nd order high pass to remove the low freq noise, and a 6th order lowpass (either sallen key or multiple feedback topology).
This could be done with a quad opamp IC "easily".
That all sounds about right.
Simplicity is reasonably important to me — so being able to do it with a quad opamp would be good.
A few thoughts and suggestions.
You can get off-the-shelf switched capacitor based filters that are more or less a single chip solution with a few setup pins. I wonder if that might work for your application.
You mention audio- What is the source signal's bandwidth? A synth? I wouldn't rely on the internal DAC for that unless you purposely want 8-bit or old school ensoniq sampler type sounds.
If it's wav or similar audio you just need some low pass. I doubt it would have to be anything exotic or expensive. 12dB/oct from one op amp should do the trick.
If you ARE building a synth, why not incorporate a proper synth diode ladder filter or whatnot and use PWM from the teensy to create the control voltages?
What is your application?
WAV playback — but synth stuff would be useful too.
Originally Posted by imaradiostar
I don't mind slightly lo-fi.