[sdiy] Low Pass filters and musically useful frequency range

[Tom Wiltshire]

> 1. As a general proposition and in a purely subjective context, what is the
> lowest frequency that is musically useful?  At some point most waveforms
> start to sound like clicks and pops. Subwoofers can pound your
> proprioceptive system and add a useful effect I suppose but "how low can you
> go" and still be musical?

Bass notes are still pretty useful at 100Hz. 50/60Hz is clearly audible as a "tone" for better or worse. I find that pitch perception doesn't really drop off until you get down to 20 or 25Hz, although it's much easier to hear a square wave at that frequency than a sine because of the harmonics much higher up. 10Hz is definitely "off the bottom of audio". Subwoofers at that kind of frequency are felt not heard, as you point out.

The usual "20Hz to 20KHz" or "25Hz to 25KHz" is still a pretty good guideline.

> 2. Why would Moog add such a high pass filter to the 914? I can see blocking
> DC, but why worry about 10 Hz getting through? Does it have to do with being
> musically useful? I don't think this high pass filter was in the 907, so why
> add it to the 914?

You'd add it to block DC, and you'd set the frequency as high as you could without cutting frequencies of interest to keep the capacitor involved reasonably small and reasonably cheap. So 10Hz is fairly low. I'd probably have halved the value myself. I can cope with a 3dB cut at 20Hz.

HTH,
Tom