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Tyme Sefari II feedback, polarity
MUFF WIGGLER Forum Index -> The Harvestman  
Author Tyme Sefari II feedback, polarity
MrBiggs
I've had this TS2 for years now, and I use it often. Almost all the time. But something I've never really figured out is the feedback section, especially the polarity knob.

When I do use the feedback, I run one of the two audio-out to, like, a filter. Then that filter's output goes back into the TS2 feedback. This does predictable stuff (filtered repeat feedback). But it seems like I must be missing something. What else can you poke into that feedback input? What are some interesting patches y'all have come up with regarding Tyme Sefari feedback?

And then there's that polarity. When my feedback is getting out of hand, I'll turn the polarity to shut it down. I don't really know what it's doing. I can't tell any difference between the polarity being set at - vs being set at +.

Any ideas?
Matos
Yeah. I'm with you on that. I can't figure out what - and + does. I need to explore feedback more. Most of my experiments were rather dissapointing.
MrBiggs
I'm gonna Bump! this.

No one has figured out the polarity switch or the TS2?
And no one has interesting play-time with feedback? C'mon...
therk
Haven't done anything more than you with the feedback (stick a filter in the loop when using it as a delay). Had barely even noticed the polarity switch! d'oh!

Haven't tried this, just thinking aloud - was wondering if you could do something like stick a square wave oscillator output into the tap tempo input and another output from the same oscillator into the audio input so could effectively sample a single cycle of a waveform. Then record whilst mangling via feedback (which might make the polarity switch useful too). Dunno how fast the tap tempo will go tho - no doubt nothing like that fast!
therk
hmmm, or if tap tempo won't go fast enough, perhaps get a similar effect by sticking the square wave in the direction input instead, so it continually goes forward/backwards over the same tiny bit of the buffer....

...always get these ideas at work when can't try them out! d'oh!
MrBiggs
What would polarity do in this case? What exactly is feedback polarity?
therk
Presume it just inverts whatever you stick in the feedback input, but that's just a guess...
MrBiggs
therk wrote:
Presume it just inverts whatever you stick in the feedback input, but that's just a guess...


You're probably right, but why would that matter? An inverted audio signal still sounds like the same audio signal unless it's run in parallel with the original. And then it's just quieter.

Whether it's + or -, I've not detected a difference in the sound.

And again, there's gotta be something more there than just a filtered delay.
therk
Well it matter if you did somehow manage to get the delay time down to being about the same as a single cycle in a wave. In that case if you've got positive polarity (i.e. feed exactly the same signal back in), it's should gain in volume when combined with original, and if you've got negative polarity it should cancel out.

But yeah, normal usage as just feedback path in a bog standard delay can't see you'd ever care.

Will try and find time to have a play with above ideas in the next day or two to see if there's anything in it, or I'm just talking carp smile
therk
Just been playing with it a bit. Can't get the polarity switch to have the slightest effect on *anything*, so no idea what that's for, however...

...the tap tempo does seem to go well into audio rates, so can get some lovely glitchy karplus-strong-ish kind of sounds by feeding square wave out of oscillator into tap tempo, anything in audio input, then feedback thru a filter. Loop, record and play all switched on.

This is with feedback going thru a Cwejman DMF2. It was very sensitive to the gain on the input to the DMF2 (that big spike in the middle is when I went a bit crazy turning it up!). First bit the saw out of a Hertz Donut into the input. Second bit is with the input removed - just the feedback loop going by itself. If I take the filter out the loop it dies away without the signal - guess it needs a bit of gain in the loop. Adjust pitch by changing pitch of square wave into tap tempo... play around with sample rate for extra glitches... nuts!

[s]http://soundcloud.com/therk/tyme-seferi-madness[/s]
MrBiggs
therk wrote:
If I take the filter out the loop it dies away without the signal - guess it needs a bit of gain in the loop.


Yeah this.

I can only get it to feedback when something is plugged into the feedback input. I've had some success with one of the outputs straight to feedback, but yeah I think a little gain helps. It definitely doesn't feedback on itself without that jack filled.

Good demo thanks.
Ras Thavas
Feedback polarity should be most notable with the TSII set to really short delay times, i.e. in the flanging range and just a little past that. Typically negative feedback (it's just inverting the audio as it recycles) gives a slightly different sound, kind of an "octave up sounding" resonance compared to normal feedback. That's why many stompbox flangers have a switch for positive or negative feedback.

Using the negative polarity should help prevent runaway oscillation in some cases too at longer delay times, though that hasn't been as obvious to me when using the TSII.
dude
i have no idea...

would love to hear why guv likes -polarity. i think frequency shifter type stuff will have different results with +/-? and there is that pitch shifter function (if you have the asot (which i do not)).

anyway, this module is pretty perfect imo. just got another one. had mk1 long ago. loved it but in and out of euro so it never stuck around. now i have it next to phonogene and they are pretty tight friends!

also the monome modules seem to really like tyme sefari. and that hikri sine oscillator comes to big big life between monome control coupled with tyme sefari processing!
robotopsy
I bet the polarity switch is to invert the feedback signal ... it could be great for phase cancelation I guess !?!?!?!?! d'oh! seriously, i just don't get it oops help
c0rpse
I use it to kill the feedback when it starts self oscillating.
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