---
title: M5Stack Cardputer-ADV plays a loud constant whine over all audio (ES8311, Arduino M5Unified)
date: 2026-06-14
summary: On a Cardputer-ADV with custom Arduino firmware, every sound (test tone or MP3) had a loud constant whine on top. The speaker ran a mono I2S frame, so BCLK was half what M5Unified's fixed ES8311 clock divider expects. Setting spk_cfg.stereo = true fixed it.
tags: m5stack, cardputer, es8311, esp32, arduino, audio
environment: M5Stack Cardputer-ADV (ESP32-S3, ES8311 codec); Arduino via PlatformIO, platform espressif32@6.9.0 (ESP-IDF 4.4); M5Cardputer + M5Unified; ESP8266Audio 1.9.7
author: shaun, written up with Claude
status: published
---

## Symptoms

Custom Arduino firmware on an M5Stack **Cardputer-ADV** (an MP3 player sketch built on
M5Cardputer / M5Unified and ESP8266Audio) produced a **loud, constant whine over all
audio**:

- the same with a generated test tone and with MP3 playback,
- also when running on battery,
- at every sample rate tried.

The pitch of the actual audio was correct; only the added tone was wrong. The stock UIFlow
firmware plays through the same ES8311 codec cleanly, which showed it was a configuration
problem, not hardware.

## Root cause

A clock mismatch between the I2S frame and the codec's clock divider:

- The speaker was configured **mono**, so the I2S frame was 16 bits per sample period:
  BCLK = fs × 16 = **768 kHz** at 48 kHz.
- M5Unified initialises the ES8311 with a **fixed clock divider** (register `0x02 = 0x18`)
  that assumes **BCLK = 1.536 MHz** (a 32-bit stereo frame).
- With BCLK at half the expected rate, the DAC master clock ended up about **2× off**, which produced the constant tone. The audio pitch stayed right because
  LRCK still locked the sample rate.

The fix below confirms the mechanism. Register-level changes did **not** help: reprogramming
the ES8311 oversampling (OSR) and bias settings, and even a full ESP-ADF-style codec init,
left the whine in place. It took about a dozen reflashes to find.

## Fix

Configure the speaker as **stereo** before starting it. That gives a 32-bit frame and
BCLK = 1.536 MHz, which matches the divider:

```cpp
auto spk_cfg = M5Cardputer.Speaker.config();
spk_cfg.stereo = true;          // 32-bit I2S frame -> BCLK 1.536 MHz at 48 kHz
M5Cardputer.Speaker.config(spk_cfg);
M5Cardputer.Speaker.begin();
```

`spk_cfg.stereo = true` was the whole fix; no codec registers needed changing. The
`config()` read-modify-write lines are the usual M5Unified pattern; the line that matters
is setting `stereo` before `Speaker.begin()`.