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Audio playback using FPU and DMA on LM4F120H5QR

kishore kedari
Prodigy 50 points

Hai Every one ,

I am working on project where I have to generate the audio data and apply the same to the GSM modem.

The same is fulfilled using PWM on single pin of LM4F120H5QR along with L-C Low pass filter and pushing audio data from SD card using timer at regular intervals.

Audio which I generated using the above method looks good when hearing with speakers and here is the problem when I am applying the same to the GSM modem and hearing on other subscriber end the same audio is very bad.

The reason is simple MIC+ ,MIC- of GSM modem will accept the continuous wave of Analog data but I am feeding digital sampled data on which GSM modem will apply some other DSP techniques I guess.

So is there any way to generate the continuous waveform of analog(sine wave) corresponding to the audio data using Floating Point Unit along with IQMATH Library and DMA for data feeding from SD card.

Any suggestion is highly appreciated thanks in advanced.

Kishore kedari

  • TI__Genius 10650 points

    We're going to need more information (and pictures) of your circuit, the speaker and the modem. Please send them. In regards to the speaker vs. modem, it makes sense that the sound would be very different.

    When playing through the speaker, are you going through an amplifier or playing on a small high impedance speaker?  The speaker is probably filtering for general audio (music) while the modem is probably filtering for voice.  The passable frequency bands are very different for the two.

    A quick thing you can try is connecting a resistor that matches the impedance of your speaker/amplifier between the audio output and ground before it goes to the modem.  This is a quick and dirty way of emulating the filtering being done by the speaker/amplifier before the audio is passed on to the modem.