I2S: odd codec output when using single channel (IDFGH-3682)

[boborjan2]

• Development Kit: ESP32-LyraT (4.3)
• Kit version (for WroverKit/PicoKit/DevKitC): 4.3
• Module or chip used: ESP32-WROVER-B
• IDF version (run git describe --tags to find it): v4.2-dev-1206-g741960d5c
• Build System: make
• Compiler version (run xtensa-esp32-elf-gcc --version to find it): (crosstool-NG esp-2020r1) 8.2.0
• Operating System: Linux
• Using an IDE?: No
• Power Supply: USB/external 5V (does not matter)

Problem Description

When setting I2S configuration to single channel (using a stereo codec), and feeding i2s with mono sample data, output changes according to the screenshots below. Note that this also happens when using internal DAC. Stereo: Mono:

This behavior is easier to notice when signal frequency is closer to sampling freq.

Expected Behavior

The signals should be the same

Actual Behavior

Signals differ.

Steps to reproduce

I am using the i2s example provided by ESP-IDF. I modified that example to 1) run on LyraT-4.3, 2) to produce mono signal 3) to test different frequencies, like 500Hz. I made this change because on higher frequencies, the issue is easier to observe.

Code to reproduce this issue

The code is mostly (99%) from i2s example from ESP-IDF. [GIST] https://gist.github.com/boborjan2/bdf3ca0a99345e20aa364c9eb61557b2

You need to #define/#undef macro "MONO" at the beginning of the file.

// If your code is longer than 30 lines, GIST is preferred.

Debug Logs

None, please check screenshots.

[boborjan2]

I forgot one detail: the scope measurements were taken at the "phone jack" output of the LyraT-4.3 board with 32Ohm stereo headphones plugged in. Note: the signal looks the same with other (smaller) loads as well.

[Alvin1Zhang]

Thanks for reporting, we will look into.