This is the latest in a series of empirical explorations of the Octatrack’s effects parameters – previous installments covered the ring modulation behavior of the Lo-Fi effect and the frequency mappings of the Equalizer’s shelving and parametric mid bands.
This one looks at the Filter effect. The writeup covers tuning the low-pass filter (WDTH parameter), tuning the high-pass filter (BASE parameter), and using both together as a resonant bandpass with musically defined bandwidth. There are chromatic tuning tables for both filters spanning B1 through A7, plus a note on using the LFO Designer to get sub-step precision on the cutoff frequency.
For bandpass, tune Base and decide on the offset you want for Width. One octave is about 11, two is about 21, three is about 32, and four octaves is about 42.
I’ll post some recorded samples of different things i’m doing with. Synthesis ideas, Moog MuRF-like things, etc. it is a lot of fun.
Edit: I’m laughing at myself because I just noticed that they’re basically the same table. I hadn’t noticed that before. They probably are the same table inside the OT and this is revealing the measurement error in my approach. That simplifies things!
Some simple synthesis sounds. These all use a pink noise sample as the source, then do variants of the tuned filter. Same melody on all filters.
0:00-0:35 - tuned high pass with three different REL values
0:35-1:10 - tuned low pass with three different REL values
1:10-2:07 - tuned band pass going through four (?) different bandwidths
2:07-end - exploring the filter envelope and the amp envelope
The “low” table was done by changing WDTH with BASE=0. The “high” table was done by changing BASE with WDTH=127. It seems like they yield basically the same tuning.
If I didn’t mention it before, when folks move to tune the bandpass, the tuning applies to BASE.
Tuning the Equalizer could be interesting. It isn’t really a perceived pitch, but you could sculpt the sound more precisely. For example, imagine a bandpass that allows C3-C7 through. You could probably figure out a way to carve out C5-C6, boost C3, or similar. It would be a bit fussy to do on Octatrack, but MIDI control could really open it up.
The tuned filter sounds really nice going into the ring mod and/or comb filter.
You can get pretty surgical if you’re willing to stack several Equalizer plugins. A few at the same middle frequency, one below BASE, and one to the right of BASE+WDTH.
