Help me design an audio delay circuit

[mikerbot]

Hello, I'm attempting to design an audio delay circuit. While electronic engineering is not my specialty, I can solder like a mad man and I have a general idea of what's going on. I was wondering if anyone would be willing to help me along. The thing needs to have audio in (rca and 1/8" mini) and audio out. Adjustable delay from 0-12 seconds (more the better, but 15 would be over kill). .5 second steps would be fine, infinite would be better. Both battery and adapter powered would be nice. It should be small (walkman sized). On/off/bypass switch (of course) and it should be as cheap as possible (of course). I explained this to a guy I know in Ohio, he gave me this:

"If I understand what you're looking to do, this could be done with an ADC, some memory to act as a buffer, and back to analog via DAC. Not really all that complicated. Small pause on startup to fill the buffer. Use an encoder (or even a pot) to set the delay value in the PIC that would be shifting the data out of memory to the DAC. There might be an even easier approach using some analog circuit, but it would be pretty easy to do it via digital/analog converter ICs."

I understand the very basic theory behind most of that paragraph (and could figure out the rest.) The biggest conceptual problem I have with it is "some memory to act as a buffer." Thanks for your time.

-Mike.

-This is a re-post from the newbie section, I hope thats OK with everyone. Thanks again.-

 

[sunking]

delay circuit for audio

what he said is you use the memory to hold the data and send them out in the right time.

 

[mikerbot]

pic audio delay

Well yes, but actual implementation of a memory chip is something I've never done.

 

[Iouri]

audio delay schematic

Also can be good idea to learn FPGA, Xilinx and Altera have those board, with audio CODECs on it, besides the delay, you can also impplimet different kind of audio effects....
Just try it

 

[mikerbot]

adjustable audio delay circuit

Really! That is interesting. I can't find the boards on Xilinx or @ltera's sites, perhaps I should call them tommorow. Thanks

Added after 15 minutes:

Ya know, if anyone wanted to just whip me up a schematic, I would be willing to compensate. Make me an offer, if that's your sorta thing.

 

[echo47]

audio delay circuits

On the Xilinx homepage, click "Development Boards" then "Online Store Development Boards".

You didn't say how much audio quality you need, but an inexpensive way to get started with FPGA is to buy the Spartan-3 Starter Kit ($99 US) from Xilinx (WebPACK development software included), and then small accessory boards (such as ADC, DAC, breadboard) from Digilent.
http://www.digilentinc.com/Products/Accessory.cfm

However, those are unexciting ADC and DAC chips. The more expensive boards have nicer built-in features. Here's a serious board, although costs $500 US:
**broken link removed**

Tons more choices (big shopping adventure):
http://www.fpga-faq.org/FPGA_Boards.shtml

Beware of possibly steep learning curve!

 

[mikerbot]

Audio Delay Circuit

Oh good lord, steep learning curve indeed. Sorry for not mentioning this earlier, I only need quality acceptable for voice.

 

[erasmocf]

Audio Delay Circuit

mikerbot,
the analog way to do this is almost impossible to be implemented, because make an analog delay you have to put in series a lot of stages with intrinsic delay, like buffers. In your case, where you need a delay of 12 seconds (infinite comparing with each buffer delay) you gonna have hundreds of thousands of buffers to do this job. Even if you make this circuit, the noise produced by this amount of stages will be prohibitively large.

The only way is to this is in the digital domain. Using an FPGA kit is a good idea. Here you will only need to learn a HDL language (verilog or vhdl), everything else is already implemented. Just pay attention to the FPGA kit's memory size.

 

[betwixt]

Re: Audio Delay Circuit

This getting very over-complicated.

You can get bucket brigade delay lines (aka charge coupled devices or CCD) which are designed to delay audio signals but they are expensive and are only good for a few milliseconds delay. Fine if you want reverb or short echo but nowhere near long enough for 15 seconds. They are also noisy so if you chain one after another to get long delays you tend to get nothing but hiss out of the last stage!

By far the simple solution is to digitize the voice using an ADC chip, use a microprocessor to store it in a static memory chip. Move along to the next memory address and store the next ADC sample, when you reach the end of the memory go back to its beginning. Basically you are leaving a trail of samples along the length of the memory. Now read back a memory address and feed the value into a DAC to reproduce it's analog equivalent, move to the next address and repeat. Keep going until to end of memory and start at the beginning again. You are reading back and restoring the trail of samples you made. The amount of delay is set by how far along the trail from the storage address you read from. Closer addresses give shorter delays. The longest delay is set by the size of memory.

Given that the process is continuous writing and reading, you might be able to use dynamic memories DRAM (they get amnesia if you don't use them for a more than a few milliseconds) which are cheaper and available with much higher capacity.

Brian.