Prop Audio Delay?

Benj

Hello,

I bought a few props about a year ago and never got around to finding a project to use them in. I think I might have something now, but have no idea where to really begin or if someone has already done something like this that I can learn about.

I would like to create a device that can take a live audio input signal, buffer it, and then output it with a variable delay. For instance, it would play back with a delay of 0 - 20 seconds that the user can select with a dial. I would want it to work continuously, not just play back a recorded sound.

Any help in pointing me in the right direction would be appreciated.

Sapieha

Hi Benj.

You can search for ...... "Stomp" on forum.

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Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

Paul Baker

Hi Benj, you will need to do some calculations to figure out how much memory you need, you need to know the maximum delay (20 seconds), your sampling speed and the bit depth. These three numbers are combined in the formula (max length in seconds) * (samples/second) * (number of bytes per sample). This number indicates what size memory you will need in order to buffer.

There's no way around it, you are going to need to add external memory in order to store all the information. What you want to do is entirely possible, take a look at the Open Stomp Coyote-1 (this is what Sapieha is talking about), it does looping record and playback (and effects, but thats not pertainent to the current discussion) using the Propeller and extra SRAM.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 9/24/2008 4:57:54 PM GMT

Beau Schwabe

Benj,

Depending on your exact Audio delay requirements, the following link might be helpful.· This link implements a Halloween·Echo effect, but basically it creates a FIFO delay buffer that keeps filling itself with some amount of decay from the original signal.


http://forums.parallax.com/showthread.php?p=676274

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Benj

Great, thank you. All of the above examples seem to use the Demo Board Rev. C and I happen to have the Proto Board, so I don't have the microphone input or the MAX4411ETP for audio out. I did a search for the MAX4411ETP and I can't seem to find it anywhere that sells them one at a time. I am not sure I need one or both of them for my prototype. I would like to have line level input (not microphone), like from a sound card, and the output connected to a set of amplified speakers (like computer speakers). I assume I would still need something equivalent to the MAX4411ETP for output, but can someone point me in the right direction of how the schematic would be different if I used a 1/8" stereo jack as input instead of the microphone jack? Also, are there any recommended substitutes for the MAX4411ETP?

EDIT: Maybe I don't need the MAX amp if I am sending the output to an amplified speaker set?

Post Edited (Benj) : 9/24/2008 6:52:18 PM GMT

Ariba

You don't need the MAX, or another Amplifier. Just use a circuit like this for the DAC:

                         +
OutPin ────────┳───────────  Amplifier
          1.8kΩ  4.7nF  10µF
                   

With the values above, it has a bandwith of 18kHz and under 2k output restistance.

Andy