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SW4STM32 and SW4Linux fully supports the STM32MP1 asymmetric multicore Cortex/A7+M4 MPUs

   With System Workbench for Linux, Embedded Linux on the STM32MP1 family of MPUs from ST was never as simple to build and maintain, even for newcomers in the Linux world. And, if you install System Workbench for Linux in System Workbench for STM32 you can seamlessly develop and debug asymmetric applications running partly on Linux, partly on the Cortex-M4.
You can get more information from the ac6-tools website and download (registration required) various documents highlighting:

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STM32F4 DAC Audio configuration

Posted by ravi on 2016-04-14 01:09

Hello Everyone,

I have a custom board with STM32F4xx chipset DAC_OUT pin connected to audio amplifier.
I am configuring DAC with DMA and TIM6 trigger for Audio playback.
With the attached configuration code, I hear a initial click sound as I start playing audio file.
After the initial click sound, the audio file is getting played fine.

Below are the observations:
• The click is heard every time we initiate playback.
• The click is independent of the file being played.
• The click is not caused by noise on the line.
• The line is noise free before and after playback.
• The click waveform does not look analog in nature.
• The click is observable at the DAC output.
• The click is observable across multiple boards, multiple MCUs (405/446), and multiple generations of boards and electrical layouts.

Can anyone help me figuring out if there is any configuration issue or is this a known DAC issue ?

Thanks,
Ravi

dac_dma_tim.c (3.00 Kb)
dac_dma_tim.c (3.00 Kb)
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Posted by dautrevaux on 2016-04-14 06:27 France

Hi Ravi,

The click has nothing to do with the MCU or the DAC; it is inherent to your way to start playing sound. The only configuration issue could be the position of the “idle” output: it must be at the middle of the output range (thus corresponding to “no signal”); otherwise you will get a steep front (thus a click) when switching even to no-signal waveform.

However even in this case you will still hear a click if you start playing sound at full volume immediatly as going from no-signal to full-signal (even a sinus waveform), when converted in frequency space will have a wide spectrum at the beginning, heard as a click by your ear. Note that this artefact can be heard even on some high quality devices (like Bose Quiet-Comfort noise reducing headphones...)

The cleanest way to suppress the click is thus to start playing your waveform at 0 volume, then raise it progressively to full volume in a few hudrends of milliseconds.

Bernard (Ac6)

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