Reverse Delay

[rousejeremy]

   I searched around for a reverse delay schematic and came up empty handed. I noticed the posts were a couple years old, so I was wondering if anyone made any schematics of a reverse delay pedal. The Backtalk comes to mind.......

[R.G.]

A lot depends on what you mean by "reverse delay".

If you mean pre-echos before the actual sound, it is not possible to do that in real time. It violates causality.

[aziltz]

not if we stick the guitarist on a relativistic train traveling relative to the amp... but that would also introduce some insane doppler shift.  wait, thats vibrato AND reverse delay...

sorry i just had too, i'm a geek.



you can do "reverse delay" digitally, like with line 6 delays, where you play and it reverses the playback a few second later.  I'm not sure how feasible this is for a DIY build.

[rousejeremy]

A lot depends on what you mean by "reverse delay".

If you mean pre-echos before the actual sound, it is not possible to do that in real time. It violates causality.

I mean exactly what the Danelectro Backtalk does. The delays are reversed with a mix control. It's such a cool effect I'm surprised it hasn't been "reverse" engineered. 

[aziltz]

http://www.youtube.com/watch?v=oA_D4zrhcGE

at 320 this guy starts using the backtalk.  its the same as my echopark where your notes get delayed some present amount and the sound is reversed.  its done digitally.

[rousejeremy]

http://www.youtube.com/watch?v=oA_D4zrhcGE

at 320 this guy starts using the backtalk.  its the same as my echopark where your notes get delayed some present amount and the sound is reversed.  its done digitally.

Man that sounds great. I read in an older thread someone saying it was using a PT2395.

[StephenGiles]

I think it sounds rediculous - but maybe OK for pre-shagging show off time in your bedroom

[anchovie]

There was a circuit on the Experimentalists Anonymous site called the "Sandwich Echo", but their server is currently down after a hack-attack. It involved a PT2395, an external RAM chip and some CMOS logic chips (lots of XOR gates I think, messing around with the address lines between the PT2395 and the RAM). It was basically some pretty advanced modding of a regular Danelectro delay so I wouldn't be surprised if Danelectro saw the mods and marketed a new pedal with them.

Anyway, I suspect the lack of a reverse delay project is because of the complexity and the cheapness of Dano pedals. Would be easier to get a used Backtalk from Ebay and rehouse/true-bypass it according to desire.

[Br4d13y]

dano also made a wasabi-series with reverse delay, and forward delay   might take  look at that one too

[Mark Hammer]

I've written about this here a couple of times.  May as well write about it again.

True reverse-tape effects require that one use a sample and play it back in reverse order.  Analog delay can not do that.  Digital can, but it requires keeping track of when the signal began.  That is a task of a higher order.

Using reverse-delay is tricky.  Since it is often hard to anticipate how things come out, it is the sort of thing you cannot just turn on and groove with at a jam, unless one is VERY comfortable with randomness, and those around you are too.  The alternative is to plan out very carefully.  If one wants to just play linearly and superimpose a reverse-like sound, then the better option is an envelope modifying device like a Slow Gear (or its Behringer clone), a PAiA Gator, or similar.

All of that being said, there is one way of producing a sort of reverse effect using analog methods.  Let us say you have an analog delay set for a medium-short delay, like 120msec.  Set the feedback quite high, and control the final feedback level with a VCA or other electronically attenuating device (JFET, etc).  Now feed the guitar to an envelope-detector/trigger generator, and feed a trigger pulse to a slow-attack transient generator that feeds the VCA in the feedback loop.  If you dump the dry signal entirely, what you should hear is a sort of ghost-like echo sound that increases over time (for the duration of the envelope).