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Why not LPF for portamento?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Why not LPF for portamento?
Jari Jokinen
There was a topic on Muff's or elsewhere about musical portamento. Can't find it, so I start new topic.

Synth "portamento" (glide) has never sounded good to me. However, I noticed that feeding pitch CV through an DC-coupled low pass pass filter gives surprisingly good results.

Attached is a test sample of playing a software synth with QWERTY-keyboard. 1-pole LPF is used for pitch CV. As you hear, "Portamento" time is not dependent on interval. This is most noticeable in the beginning, where there is a huge upwards jump from sub-audio.

I don't know, if this can be done with an analogue filter. Not with Boogie at least. Maybe with Mankato. Anyway, I thought this is interesting.
Kent
I do it with the Mankato filter quite often. Works great and you can use all of the outputs at once for difference stuff!
cornutt
This is interesting since a conventional glide module basically is a low pass filter. I'm actually wondering if the soft synth filter algorithm isn't doing something right in the subsonic region.
Yohda
Quote:
Portamento" time is not dependent on interval. This is most noticeable in the beginning, where there is a huge upwards jump from sub-audio.

You can do time based portamento too with an ASR :

Send your keyboard cv to the ASR input, your gate to the asr trigger in, then send the first asr out to an inverser and then to a mixer, send the 2nd out of the asr to the 2nd input of the mixer.

If you play a higher note, the result voltage will be positive and if you play a lower note, the voltage will be negative.

The bigger the difference between the 2 notes, the higher the voltage (neg or pos)

This way you can use this voltage to control the speed of a VC-portamento.

Give you glide a la TB 303.
Somatic
Yohda, is ASR an Analog Shift Register ?
Yohda
Yes, that's it !
Jari Jokinen
cornutt wrote:
This is interesting since a conventional glide module basically is a low pass filter. I'm actually wondering if the soft synth filter algorithm isn't doing something right in the subsonic region.

This soft synth filter used in my example behaves similarly/correctly in audio and sub-audio ranges.

Conventional glide module like Maths or Bananalogue VCS is indeed some sort of low pass filter, but not normal XdB/oct filter: The output can't vary faster, than the set slew rate allows. However, infinitely fast (in theory) change of direction (like in triangle wave) is possible. This is different from normal filtering.
Jari Jokinen
A DC-coupled regular filter could be used to make evelope too. "1-pole_filter_EG.gif"
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