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HDMI Audio pitch not consistent between video modes

Question asked by Max Jovanovich on Dec 5, 2013
Latest reply on Feb 20, 2014 by Yixing Kong

On an i.MX6Q embedded Linux device, I have an application with two different video modes available: 1280x1024 and 800x600.  Here are the mode specs from /etc/fb.modes:

 

mode "1280x1024 60Hz 24bit"

    # D: 107.99 MHz, H: 64.281 KHz, V: 60.08 Hz

    geometry 1280 1024 1280 5120 24

    timings 9260 128 128 40 2 144 4

    hsync high

    vsync high

endmode

 

mode "800x600 59Hz 24bit"

    # D: 41.38 MHz, H: 37.754 kHz, V: 59.93 Hz

    geometry 800 600 1280 5120 24

    timings 22727 128 96 24 2 144 4

    hsync high

    vsync high

endmode

 

When I use the speaker test to generate a sine wave, e.g. using:

 

speaker-test -D plughw:0,0 --test sine

(Note: in my hardware/kernel HDMI is the only audio device.)

 

I get a different tone (pitch/frequency) depending on which video mode is selected, even though the speaker test is supposed to generate a default frequency of 440 Hz (music note A4) for the sine wave.  The difference between the two in the different video modes is easily noticeable.  Off hand, I'm not sure if or which one is correct.

 

Does anyone know why different frequencies are being output?

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