Reverse Delay: DIY ?

[carrejans]

Are there any projects on the web for some Reverse Delay?

[Mark Hammer]

No.  Reverse delay is always digital, and necessarily involves "exotic" tweaking of addressing, which in turn will involve use of delay chips with external RAM.

There was a project a number of years back, called the Polywhatsit, that appeared in Practical Electronics, providing reverse delay, but quite frankly you're far better off spending $80 on a Behringer clone of the Line 6 Echo Park that is supposed to be out this summer.

[petemoore]

   ..whhoops what mark said.
  Reverse delay...I was thinking reel to reel and turn the tape around for reverse playback where the note envelopes  [sustain and attack] are all truly reversed.
  And didn't catch the definition of 'reverse delay' a scrambling of delays made to replicate some of the feel [and add some new feel] of actual reverse playback sounds, intended for live use where you can't fake reversing time.

[mojotron]

I think one would have to find a long digital delay project first.

I think it is doable, I mean - off the top of my head I imagine that if you had a A-D converter feed a uC data, the uC stuffs it away into memory; then at some adjustable rate the uC would take the data out of memory and feed it out to a D-A converter - that could work I imagine.

Then, to reverse that sample of sound, the uC could keep 2 pointers in memory; one for data being written in and another for the reverse. The uC would write the data concurrently - into 2 mutually exclusive memory regions - assending from one pointer in one region of memory, and descending from the other pointer in another region of memory. Then to read the data out reversed, or forward, the uC only needs to pick which region to read the data going to the D-A converter to go out. The code could be simple enough to be doable - let me know when you have it done    

[Solidhex]

I don't know if it would sound very convincing but I'd be curious to hear a delay in a mix loop with a slow gear after it. Almost like a backwards guitar player answering your phrases. I guess that means I'll have to build a slow gear, a delay, and a mix loop now....

--Brad

[grolschie]

Reverse delay? Wouldn't you need a time machine to repeat the note before you even played it? 

[carrejans]

I think one would have to find a long digital delay project first.

I think it is doable, I mean - off the top of my head I imagine that if you had a A-D converter feed a uC data, the uC stuffs it away into memory; then at some adjustable rate the uC would take the data out of memory and feed it out to a D-A converter - that could work I imagine.

Then, to reverse that sample of sound, the uC could keep 2 pointers in memory; one for data being written in and another for the reverse. The uC would write the data concurrently - into 2 mutually exclusive memory regions - assending from one pointer in one region of memory, and descending from the other pointer in another region of memory. Then to read the data out reversed, or forward, the uC only needs to pick which region to read the data going to the D-A converter to go out. The code could be simple enough to be doable - let me know when you have it done    

Why has no one tried to make one? Idea for the rainy days of one of you guys? 

[carrejans]

What are the commercial available pedals anyway? And are they any good?
In the time of Jimi Hendrix; was it done with real tape?

[Mark Hammer]

You should go to a music store and try out one of the digital delay pedals that have reverse as an option.  The Boss and Line 6 pedals will do it, and I believe even Danelectro has one.  The chief logistic problem with producing reverse delay in real time is that the pedal has to know what the beginning is, and it can't know that until you've stopped playing.  With forward delay, the "beginning" is whatever lies in the first storage element of however many you have.  Same with analog forward delay.  In reverse, I may only use up 57% of the available storage space to play my phrase at the delay time selected, but the circuit won't know that until I reach the end of my phrase.  So, problem 1 is that there has to be a foolproof system for identifying where the end of the phrase is so that the circuit can figure out when to start playing the stored samples in reverse order from that point.

It's a LOT more complicated than the simple switch click makes it seem.

[StephenGiles]

You should go to a music store and try out one of the digital delay pedals that have reverse as an option.  The Boss and Line 6 pedals will do it, and I believe even Danelectro has one.  The chief logistic problem with producing reverse delay in real time is that the pedal has to know what the beginning is, and it can't know that until you've stopped playing.  With forward delay, the "beginning" is whatever lies in the first storage element of however many you have.  Same with analog forward delay.  In reverse, I may only use up 57% of the available storage space to play my phrase at the delay time selected, but the circuit won't know that until I reach the end of my phrase.  So, problem 1 is that there has to be a foolproof system for identifying where the end of the phrase is so that the circuit can figure out when to start playing the stored samples in reverse order from that point.

It's a LOT more complicated than the simple switch click makes it seem.

You've hit the nail on the head there Mark - great for impressing your girl friend before you take your clothes off, but in a band situation - bloody useless

[alex frias]

I used a BOSS rack RPS-10 ( actually a Brazilian version on a full rack under the Oliver brand, but as I saw inside, BOSS proprietary chips)for that reverse delay in real time.
Well, so I don't think it´s useless, hard to manage perhaps, as you must antecipate and figure out how it will sound when you play it if you wish to do more down-on-earth stuff.
Nowadays I'm using a Wasabi one with reverse and straight delay up to 3 seconds and a pot for high frequencies attenuation, but Dano has a Reverse-only unit, I think.
If some thinks it´s useless in a band situation I would like to recommend listening to Adrian Belew, Robert Fripp and David Torn playing live.

[carrejans]

Yeah, I've heard people play it live; and it sounded amazing. Just needs a lot of practice.
Maybe you can solve the problem with a simple footswitch. (or maybe a swell pedal) You can let the effect know when the "beginning" is. No?

[Mark Hammer]

Correct.  Feasible live, but best used for planned playing of known content, rather than improvisation.  Not unless your idea of improvisation also includes things that even YOU didn't expect.  If I was in a beatles cover band and we played "Taxman", I could use one, no problem.

Slow Gear pedals, while not at all authentic sounding as reversers, have the advantage of playing things as you spit them out, which lends itself better to improv.

[alex frias]

It will be something as a sample start, but I doubt how exactly it could help without testing it. In my JamMan i have a sample function that can be reversed when the sample phrase is triggered, but I still think the usual cycle method implemented in several projects is more efficient.

[carrejans]

It will be something as a sample start, but I doubt how exactly it could help without testing it. In my JamMan i have a sample function that can be reversed when the sample phrase is triggered, but I still think the usual cycle method implemented in several projects is more efficient.

Like in which projects?

[alex frias]

The comercial ones:
Wasabi, BOSSES, Danelctro, Line6, etc.

[dr]

.....I get a kick out of my Dano Reverse Delay-it does a pretty decent job in one-two second snippets-and it has a PT2395 in it!....other than that, I usually use the Digitech Dimension 12 in reverse mode (rackmount) wish my PDS 2020 could do that, because they can be tweaked for 8 seconds!....(not reverse of course).........dr

[grolschie]

Marshall EH-1 Echohead has reverse mode. Damn good delay for the price - just never run it on batteries. Beats the Digitech DigiDelay I reckon tonewise. Reverse mode is cool and all, but I cannot think of an application for it outside bedroom noodling.

[boyersdad]

So if the Dano has a PT chip and does reverse, why isn't there a DIY project, or why does is seem unfeasible? The other digital logic and memory involved?

[vegetanacho88]

the only info that might serve useful is in here http://www.electrosmash.com/back-talk-analysis wich gives you an insight into how the dan electro works