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DIY Digital Audio Multitrack Recorder
DIY Digital Audio Multitrack Recorder
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Old 10th September 2019, 03:08 PM   #1
digiDave is offline digiDave  United States
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Default DIY Digital Audio Multitrack Recorder

Hello diyAudio world!

A friend of mine who is blind really wants to be able to do some multitrack recording. No commercial solution (that I've found) seems adequate since the user interface in this case needs to be simple and totally tactile. So I thought I'd build an audio recorder for him. Just a "simple" 1 or 2 input, 4 track max, stereo output recorder with at least 16bit 44.1khz resolution.) I'm experienced in audio, microprocessor programming and electronics. But I haven't been able to find (or conceive of) a complete solution.

I've been looking at the ADAU1701 as the main component of this system. (I don't need much DSP processing but it has several ADCs and DACs.) I envision it working as follows (with my questions inserted.):

RECORDING:
1. microphone to analog preamp
2. preamp out to one of the ADAU1701 ADCs
3. set desired sample rate of the ADC and it will start sampling
4. Question: now the audio is in the DSP. How to I stream it to an SD card to save the audio? I would assume through one of the I2S ports. Can this be done concurrently with the sampling?
I'd probably need an external microprocessor for the file manipulation?

PLAYBACK:
1. Question: how do I read an audio file from the SD card and stream it into the ADAU1701. I assume the ADAU1701 can't do this on it's own. Somehow I need to read the file and convert it into an I2S stream for the 1701. This would require a separate microprocessor? Question: can I load more than one file and process them concurrently in the DSP?
2. Now the audio (up to 4 streams) are in the the DSP. I can process them as necessary and sum them to stereo and send out through 2 DACs for stereo.

Well, that's my strategy. Does it make sense? Thanks in advance for any thoughts, guidance.
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Old 10th September 2019, 03:52 PM   #2
Max Headroom is online now Max Headroom  Australia
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Old 10th September 2019, 03:57 PM   #3
digiDave is offline digiDave  United States
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Thanks for your reply. I realize there are very cost effective products out there but *as stated*, this is for a blind person who cannot deal with LCD screens and menu layers and a plethora of knobs.
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Old 10th September 2019, 06:04 PM   #4
Markw4 is offline Markw4  United States
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There is at least one SD library for Arduino. Apparently it works over SPI bus.
Arduino - SD
GitHub - arduino-libraries/SD: SD Library for Arduino
Guide to SD Card Module with Arduino | Random Nerd Tutorials

Perhaps even more support for doing it with RPi.

Aside from reading an SD card, it would also be necessary to decode the audio file format. Wav files are riff containers, IIRC. Searching for the file format should lead to more details. Could be there are already open source SD to I2S music playing projects out there. If so, all that might be needed could be to rewrite the user interface to work as needed for the particular application.
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Old 10th September 2019, 09:30 PM   #5
Mark Tillotson is offline Mark Tillotson
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The SPI access to an SDcard is too slow for this. You need native mode to get high data rates to/from an SDcard.
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Old 10th September 2019, 09:45 PM   #6
Markw4 is offline Markw4  United States
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Okay. That would seem to favor RPi. usb sd card reader for rpi - Google Search
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Old 11th September 2019, 12:23 AM   #7
digiDave is offline digiDave  United States
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Thanks for your input!

So you're talking about a sound card for the Raspberry Pi, correct?

I'll check into that. Hopefully there's a card with a published API.
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Old 11th September 2019, 01:19 AM   #8
Tubelab_com is offline Tubelab_com  United States
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I would look into one of the Teensy series tiny SBC's with it's companion audio adaptor. There is an SD card slot on the audio adaptor and most of the routines to do what you want already exist in the GUI based audio library. The GUI interface can do much of the coding for you and the rest is Arduino compatible code.

I have been using them for music synthesis, but there have been some SD card recording devices discussed in their forums. There is a 6 in 8 out audio board discussed in the forums that is available from OSH park. I have used it for multiple output synthesizer modules

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Old 12th September 2019, 02:19 AM   #9
digiDave is offline digiDave  United States
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The Teensy looks promising. Thanks for the suggestion! Definitely going to check that out.
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