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digital audio delay

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Dan Rodgers

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....does anyone have any simple digital audio delay schematics they would share? I have a number of different static and dynamic ram chips I could use; I have already built bucket-brigade devices before,but none have an appreciable length of more than two seconds or so.I even have some ram modules left over from my old computer......thanks!
 
I don't think that's what Dan had in mind. I think he's looking for something like DeltaLab used to make called an Effectron, although the longest delays I've seen some of those do is a little over 2 seconds. The Effectrons were rackmountable, musician's-type gear though.
 
You may already know this, but...
Digitize the audio with a clock signal whose frequency is more than twice the bandwidth of your audio, and use that clock to also drive a counter which is long enough to address as much memory as you need (or have). Think of the memory address space as being a circle, like a clock. Think of the address as a rotating pointer (the write pointer) which zooms around and around the circle, storing the audio. Generate a read pointer at the same rotation frequency, but with variable offset, by using adders or counters. This generates a rotating read pointer which chases the write pointer. The delay is a function of the write-to-read offset.
You will probably want to control the pointer offset (delay) with a microcontroller, although you could do it with standard logic parts. Static RAM would probably be a lot simpler to control than DRAM (computer memory), because of the limitations of minimum clock frequency and refresh imposed by DRAM. Some of the other trolls here may be able to refute this - it's not my strong suit.
 
gerty said:
Anybody remember the old 'reverbs' ??

You mean a "spring tank reverb"? My old Peavey guitar amp has one of those in it.
 
Spring tank....Plate ( expensive studio gear) . The original verbs were where a speaker was placed w/ a microphone in the bathroom and recorded with the live track ( that where the "bathtub reverb" phrase came from ) . The glen glen sound company came up with a long concrete hallway with a speaker at one end and a movable Mic and baffle.

Current digital technology allows for a digital delay that is only dependent on memory size. The last digitec rackmount I had ( DSP128) was a reverb with a 17 second delay .
 
TillEulenspiegel said:
Spring tank....Plate ( expensive studio gear) . The original verbs were where a speaker was placed w/ a microphone in the bathroom and recorded with the live track ( that where the "bathtub reverb" phrase came from ) . The glen glen sound company came up with a long concrete hallway with a speaker at one end and a movable Mic and baffle.

The BBC Radiophonic Workshop, one of the early pioneers of electronic music, used to use an empty basement room as an echo chamber - various microphones and speakers were positioned in the room with long cables back to the workshop.
 
Ron.....are you there?

.....I think I may have gotten hold of a partial schematic that will work with static ram,and another one with dynamic ram....In order to make the delay longer,would I need to increase ram capacity,or sample differently?....thanks!
 
Re: Ron.....are you there?

Dan Rodgers said:
.....I think I may have gotten hold of a partial schematic that will work with static ram,and another one with dynamic ram....In order to make the delay longer,would I need to increase ram capacity,or sample differently?....thanks!

Either, or both - increasing ram will increase the delay and keep quality the same, decreasing the sample rate will increase the delay, but decrease quality.

You could perhaps have the sampling rate adjustable, this way you could adjust the delay time (at the expense of quality).
 
If you do a read-modify-write to the same address, your delay can be changed by changing the modulus of your address counter, i.e., changing the point at which the address resets to zero. The other way is to do what I suggested in my previous post, and that is to have separate write and read addresses, each advancing by one with each sample, and with a variable offset between them. The first method would seem to be simpler.
 
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