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Questions about project to access audio input

Martin Klíma

May 19, 2020 18:57

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Hello, I am sorry for a naive noob question, but I was not able to find relevant information. I will be grateful if anybody can point me in the right direction.

I am trying to build a simple "disco light" setup controlled by RPi. I have chain of individually addressable ws2811 LEDs and I would like to create some visual effects based on audio input. The actual audio source is not the Raspberry, it's some other device. I will run analog audio ouput from that other device through some line splitter and one line will be plugged into an audio card on Raspberry.

Now the questions:

1. I was thinking about DAC+ ADC card for this, is that a good choice?

2. How can I access information about the incoming audio signal from my program (I am writing in plain C)? I see there is DSP toolkit project on Github, but I am afraid I don't understand how it works. Should I download SigmaStudio and create DSP program there? The datasheet does not mention DSP anyway, so it's probably not present anyway?

3. I need to use GPIO 12 pin to control my LEDs, is it possible to solder a header on DAC+ ADC?

Again, I am sorry for my ignorance on this topic and I will be grateful for any information.

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7 comments

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  HiFiBerry team May 19, 2020 19:30

  Yes, the DAC+ ADC would work for this. In your program you need to read the audio data using the ALSA API:

  https://www.alsa-project.org/wiki/Tutorials_and_Presentations
  
  You can solder a 2x20 pin header onto the DAC+ ADC. Note that soldering onto the board will void warranty.

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  Martin Klíma May 19, 2020 20:15

  Thank you for your quick response.

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  Martin Klíma May 20, 2020 11:39

  A followup question, again, I am sorry if this is something that's widely known. On the images of the board, I can see two rows of twenty holes next to the soldered ends of the header that connects the board to RPi. Are the pins from the header connected to these holes? That is, if I want to use just two pins (ground and GPIO 12), am I better off soldering a small header just for these? Or do I have to desolder the whole 2x20 header and solder a stacking header in its place?

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  HiFiBerry team May 21, 2020 05:49

  Yes, the header pins are connected to these pins. Please also read this:

  https://www.hifiberry.com/docs/hardware/gpio-usage-of-hifiberry-boards/

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  Martin Klíma May 21, 2020 08:42

  Thank you for your response. I have actually read the document before posting and I was able to verify that the pins I need are not used by HiFiBerry board, so in that respect it's a very good resource. My question was about the breakout header, as it is not mentioned in the DAC+ ADC datasheet. I've read this document:

  https://www.hifiberry.com/accessories/accessories-faq/

  that mentions stackable headers and need for de-soldering the old headers without mentioning the breakout header, hence my question. There are probably posts on the forum that clarify that, I freely admit I haven't read them all.

  Anyway, I have already ordered my DAC+ ADC card, so wish me luck.

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  Martin Klíma June 02, 2020 12:38

  Hello, I would just like to let you know that I finished my project successfully, thank you for your help.

  On a related topic, I have one more question: is it possible to pass the analog audio signal directly from input to output?

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  HiFiBerry team June 02, 2020 12:39

  Unfortunately there isn't. As DAC and ADC use different chips, the only way to route audio is via the Pi.