[sdiy] Low Pass filters and musically useful frequency range

[David Ingebretsen]

Thanks Tom,

I think I confused the issue with the "10 Hz" comment. The filter actually
hits everything below about 40 to 60 Hz which is what is curious to me. Why
not make it 20 Hz? Why make it something around 40 to 60Hz?

David


>> -----Original Message-----
>> From: Tom Wiltshire [mailto:tom at electricdruid.net]
>> Sent: Tuesday, May 06, 2014 1:32 PM
>> To: David Ingebretsen
>> Cc: 'synthdiy diy'
>> Subject: Re: [sdiy] Low Pass filters and musically useful frequency range
>> 
>> 
>> > 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