audio files plays in slow mo

[crack-coder]

I was adding files to the folder to play and when I unplugged the pi I was using to move my setup, I started the pi back up and when I turned on the radio to hear the music I put on it was in slow mo. I tried all of the music I put on and I get the same result. I even dragged the wavs over to my computer and they would play normally. I didn't do anything new and the ran the same command as before and now the files don't play at full speed.

[mouseroot]

I was having this issue as well, even the star-wars.wav file was playing at a delayed rate, after headaches, the answer lies with the DMA setting, in the readme is says that if you use 255 it will disable the DMA channel, this fixed all my issues, hope it helps you too...

also, I was not really sure what DMA channel setting does, but for me 0, 1 gives the same slow audio, 2 seems like its a tad faster, but still too slow, i didn't get any different results from any other settings (0-15) and 15 giving no audio at all.

sudo sox NightVale_174.mp3 -r 44050 -c 1 -t wav - | sudo ./fm_transmitter -f 94.1 -d 255 -

Originally I had thought perhaps sox and even ffmpeg was not producing the proper audio formats, but using WinSCP and pulling the files onto my windows machine, the translated files were perfecly fine

infact after some digging i learned that you can use the soxi command to get a sanity check on the output of the wav files if you try to convert them first before using the transmitter, though to be honest, its kinda of easier to just use the stdin and play mp3 files instead of having to convert them first

pi@retropie:~/FM/fm_transmitter $ soxi ../sounds/star-wars.wav

Input File     : '../sounds/star-wars.wav'
Channels       : 1
Sample Rate    : 22050
Precision      : 16-bit
Duration       : 00:02:20.00 = 3087000 samples ~ 10500 CDDA sectors
File Size      : 6.17M
Bit Rate       : 353k
Sample Encoding: 16-bit Signed Integer PCM

pi@retropie:~/FM/fm_transmitter $ soxi nv2.wav

Input File     : 'nv2.wav'
Channels       : 1
Sample Rate    : 22050
Precision      : 16-bit
Duration       : 00:23:12.20 = 30697920 samples ~ 104415 CDDA sectors
File Size      : 61.4M
Bit Rate       : 353k
Sample Encoding: 16-bit Signed Integer PCM

pi@retropie:~/FM/fm_transmitter $

After this sanity check i started to dig into the existing settings and thats when i saw the DMA option.

[JadenJSJ]

@crack-coder and @mouseroot
I think i found a temporary fix, although kinda hacky it works.
It works by increasing the pitch and increasing the speed of the music.
I also found that using 44100 sample rate yields better quality, so I used it here

ffmpeg -i 米津玄師.m4a -ac 1 -af "asetrate=44100*(44100/22050),aresample=44100" -f wav -bitexact -acodec pcm_s16le - | sudo ./fm_transmitter -f 105.2 -b 230 -

[markondej]

this problem occur mainly on RPi 4, as some other hardware is messing PWM clock and DMA is triggered slower than expected. I found this may be related to ARM cores frequency governor, and by disabling it problem can be solved. Please try typing:

echo "powersave"| sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

[JadenJSJ]

@markondej I am using a Raspberry Pi 3B+ and I have the issue

Please try typing:

'''echo "powersave"| sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor'''

Dosen't work for me, the sound is still slowed down

I also tried using the parameter below
'-d 255'
It didn't work, it would say bus error, and exit.

[anattolia]

I had the same problem and I guess it's a sample rate frequency issue, although I don't know exactly why this happens.

My solution: to duplicate the sampleRate in the PMWController class (transmitter.cpp file) when you set the parameters of the ClockDevice.
As you can see, i literally just multiplied the value (sampleRate) by 2:

After saving the changes you have to build the executable again with the make command.