Rev C audio shield on a Teensy 4.1-codec answers on I2C but output is noise + heavily distorted audio

I

ianni992

Member
Rev C audio shield (the Teensy 3.x one) on a Teensy 4.1. Pinouts don't line up so it's wired point to point:

Code: 
shield 11 (MCLK)  -> Teensy 23
shield  9 (BCLK)  -> Teensy 21
shield 23 (LRCLK) -> Teensy 20
shield 22 (DIN)   -> Teensy 7
shield 19 (SCL)   -> Teensy 19
shield 18 (SDA)   -> Teensy 18
plus 3.3V and GND

DOUT not connected, playback only. Wires about 10 cm, through a breadboard.

The codec answers on I2C, CHIP_ID reads back correctly, config verifies after enable().

What I get out is a constant noise floor with the audio just barely audible underneath, heavily distorted - it sounds synthetic, like a badly aliased version of the signal. Volume is low too.

What I've tried:

- Minimal stock sketch (USB audio in -> AudioOutputI2S, enable(), volume(0.6)), no code of my own. Same result.
- CHIP_I2S_CTRL stepped through half a dozen combinations (32Fs/64Fs, 16/24/32 bit, left and right justified, inverted clock). No audible difference between any of them.
- Dedicated ground twisted with MCLK, second one with the BCLK/LRCLK/DIN bundle. No change.
- USB power and wall supply. Same both ways.

One thing does change it: touching or pressing the MCLK wire while it plays raises the pitch, still distorted. Already swapped that wire, still does it.

Anyone seen this combination - I2C fine, audio mangled? And is a breadboard usable at all for an 11 MHz MCLK over 10 cm?

Thanks
 
Hi Paul, I don't know if you understand wiring. the 3.3 is connected to pin 3.3 of the shield
thanks

IMG_2560.jpg
 
Check MCLK. It's supposed to connect to pin 11 on the Rev C audio shield.

From the photo, looks like it might be connected to pin 12.

1785371653734.png
 
It may be an optical illusion but, those headers on Audio adaptor appear to extend beyond the Audio board pcb. Hence the yellow wire is connected to nothing.
 
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