PWM frequency for Audio generation.

sri-sri

Other Parts Discussed in Thread: MSP430G2403

Hi all,

I have this code working fine to generate audio via PWM. The audio file is a WAV file generated from Audacity software with 16 KSPS frequency, 8 Bit mono PCM. I have stored this file into EEPROM and used msp430g2403 to generate PWM.

Now my doubt is.

1. What should be the PWM frequency to make this wav file audible (clearly).

2. I was successful in reproducing the audio @ 32KHZ & 64 KHZ of PWM frequency from MIcro.

3. I taught that I could get it working at 16 KHZ as well. but some how the audio is stretched (which says to me that the PWM frequency is not right)

is there a formula to calculate PWM frequency required to generate audio from wav files.?

Thanks in advance.

Sri.

over 10 years ago

0 Todd Anderson78572 over 10 years ago

Guru 14640 points

Sri:

Here is a link that may help: http://www.ti.com/lit/an/slaa405a/slaa405a.pdf

0 sri-sri over 10 years ago in reply to Todd Anderson78572

Genius 4140 points

Hi Todd,
I have read this doc but it dint really explain/mention the thing that I wanted.

0 Jace H over 10 years ago in reply to sri-sri

TI__Guru 56685 points

Hello Sri,

I have written a TI Design that features Voice Band Audio using a PWM DAC. It should be released by the end of this week. The document will go into more detail and provide example code for different MSP430s at several different frequencies. Basically the information you are looking for is the following:

F_timer = F_playback X (2^n) where:
F_timer is the required PWM timer frequency
F_playback is the PWM signal frequency, which is the DAC update rate
n is the desired resolution of the DAC in bits.

For your project you have 16kHz X 2^8 = ~4.08MHz. This means you would have to run you Timer at 4MHz in order to get an 8bit, 16kHz sound out of it. You must also ensure a new sample is loaded into the Timer CCR register before a new 16kHz tick occurs. I do this via interrupts. Please look for my TI Design that will be coming out soon that includes more information and example code.

Regards,

0 sri-sri over 10 years ago in reply to Jace H

Genius 4140 points

Hello Jace H,

Thank you so much.

Will you please let me know as of, how & where to look up for your upcoming TI Design note? If possible will you be able to post the link to my inbox or in this Thread, when it is ready? Please :)

Thank you,
Sri.

0 Jace H over 10 years ago in reply to sri-sri

TI__Guru 56685 points

All,

The TI Design I mentioned is now live. Check it out at the link below:

http://www.ti.com/tool/tidm-voicebandaudio

Regards,

0 Dennis Eichmann over 10 years ago in reply to Jace H

Guru 74080 points

This is quite an interesting document. Thanks for that!

Dennis

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PWM frequency for Audio generation.