Using the Shruthi-1 as filter for external signals

I’m sorry if this is a dumb question (and it probably is), but this is driving me crazy.

I’d like to use my Shruthi as a filter for external signals. The manual states that this signal goes through the VCA, so the envelope controlling that needs to be triggered by MIDI or sequencer. But there are those “in>xxx” patches that just route the signal through the filter. How do those patches open the VCA? I think I’ve looked at every single parameter therein but haven’t found the secret ingredient – it’s not the arpeggiator, and it’s not the sequencer, and it sure isn’t MIDI. Can someone please enlighten me?

Press and hold button 1for 10 seconds. This latches the gate.

> Can someone please enlighten me?

Check the modulation matrix. All standard synth patches have the envelope routed to the VCA, in modulation cord #9. The in> patches don’t.

Thanks a lot! I just saw that I somehow double-posted this… sorry for that!

To revive this age-old thread… I have been testing external filtering on my SMR4 Shruthi XT for a bit, and I’m still having troubles. I am routing the audio out through a send channel on my mixer (Behringer UFX-1604).
First of all, it is very easy to overdrive the input; the external signal is much quieter than the Shruthi’s oscillators if not overdriven so I constantly have to fiddle with the controls. A second Shruthi has the same problem – is this normal?
Second, I can’t seem to get the filter to open fully without modifiers. With all modifiers at 0 and the filter at 127, it sounds like it is half-closed. The only way I found to get it to open fully is to feed MIDI in at the same time and use Env1 with Sustain at full. I must be doing something wrong, can someone enlighten me?

> is this normal?

Yes. An oscillator waveform will always be at full amplitude, while a general audio source (fully enveloped signal) will be at maximum amplitude only at rare moments. If you add more gain, there will be awful clipping at these rare moments. A compressor could help.

So if you use the external audio input in addition to the internal oscillators, it’s better to feed the input a “solid” material like an external oscillator signal.

> I must be doing something wrong, can someone enlighten me?

Key-tracking is… the key.

You can disable it by using an offset to cutoff in the mod matrix (or negative offset from note). Or by triggering (just once) a note.

> So if you use the external audio input in addition to the internal oscillators, it’s better to feed the input a “solid” material like an external oscillator signal.

OK, this makes sense. Thanks!

> You can disable it by using an offset to cutoff in the mod matrix (or negative offset from note). Or by triggering (just once) a note.

Neither offset works for me. Positive not>cut closes the filter, anything lower than 0 has no effect. Negative ofs>cut closes the filter, anything higher han 0 has no effect. Triggering a note just once opens the filter… but it would be nice if this were not necessary. (This is firmware 1.01 by the way.)

I’ll look into this.

Here’s what happens: filter has keytracking. Keytracking is determined by the last played note. When you boot the synth, last played note = 0 (which allows the synth to know that portamento and co won’t have to be active on the first note you play).

I need to add a special case in the keytracking code to disable keytracking when last played note = 0.

Easy fix, will come later.

Hi! I was trying the same thing was this fixed? I wanted to use it as filter sometimes so what should I do to make this work easily?

Thanks!

Here’s a file with the fix.

Wow that was a very quick answer! Impressed how fast you are man Did you have an old threat on how to put the audio in? I saw some people talking about not using more than 63 on mod matrix etc? Thanks a lot

This is very cool, thank you! OTOH does it not break something when you actually play note 0?

> does it not break something when you actually play note 0?

No, it behaves as if you have released a middle C when the synth is powered on, so you get “neutral” keytracking.

bjoern what is your setting for getting the audio right thru? Thanks!

has the code been committed yet? Would love to add this to my personal build.

Yes, it’s been on github for a loooong time.