Integrating SD Recording with 8-band WDRC

nraj · July 29, 2021, 12:13pm

Hello,

Currently, I am trying to integrate the SD card recording code (taken from this Tympan library example code) with the 8-band WDRC example code to record the input data on SD card on the Rev D. However, after I set the SD card writer to the “Prepared” state and then start the recording, the Tympan hangs up and the red LED is constantly on (which corresponds to none of the SD card states), and the i2s output is just a constant sound. Has anyone tried working on this before? Or, is this due to the Rev D’s CPU constraints?

Thanks,
Nithin

erk1313 · July 31, 2021, 6:35pm

I believe we have an existing code that combines 8-band WDRC with SD writing. Let me check for you.

In the meantime, you can look at this example which is 8-band WDRC meant for digital mics and demonstrates SD card writing:

nraj · July 29, 2021, 3:50pm

UPDATE :
So, when I decrease the number of bands to 3 from 8 (24,000 Hz sampling rate, 128 audio block size), the SD card writing works, so I guess this is due to the Rev D’s constraints.

erk1313 · July 29, 2021, 3:50pm

The Rev-D is a bit limited in processing power for 8-band FIR (which takes about 80-85% of the CPU). Can you share your code?

To outline the steps of grafting on the SD card writing.

instantiate the audio writer class
virtually connect it into the audio chain
add the setup and servicing code
add some sort of user controls via Serial Monitor or Phone App to start/stop the recording.

Here is the most straightforward example to follow:

github.com

Tympan/Tympan_Library/blob/master/examples/02-Utility/SDWriting_01_StereoAudio/SDWriting_01_StereoAudio.ino

/*
   SDWriting_01_StereoAudio

   Digitizes two channels and records to SD card.

      >>> START recording by having potentiometer turned above half-way
      >>> STOP recording by having potentiometer turned below half-way

   Set Tympan Rev C or D.  Program in Arduino IDE as a Teensy 3.6.

   Set Tympan Rev E.  Program in Arduino IDE as a Teensy 4.1.

   Uses super-fast SD library that is original from Greiman, but which
      has been forked, made compatible with the Teensy Audio library, and
      included as part of the Tympan Library.

   Created: Chip Audette, OpenAudio, March 2018
    Jun 2018: updated for Tympan RevC or RevD
    Jun 2018: updated to add automatic mic detection
    Jul 2021: updated to support Tympan RevE

This file has been truncated. show original

Here are some things you could try:

Have you verified the original 8-band WDRC code runs on your Tympan Rev-D?
In your code, can you comment out the WDRC code and change the patchcords to route audio directly to SD card (bypassing the WDRC?)

erk1313 · July 29, 2021, 3:52pm

Ah, I see you have the 3-band WDRC working with SD writing. I’ll make a note of this limitation for the WDRC 8-band.

nraj · July 29, 2021, 4:38pm

UPDATE :
SD card writing works with 8-band WDRC if we manually decrease the buffer size for the SD writer object to around 60000 (default is 150000), using audioSDWriter.allocateBuffer(60000); in the setup code for the SD writer object.

chipaudette · July 30, 2021, 12:54am

Nice work finding solutions! Woo-hoo!!