How to pad signal

[GuillaumeLeclerc]

Hello,

I have 16bits per sample signal and I would like to convert it to I2S 24bits with 8 bits of padding at the right. What is the best strategy to achieve this? I tried modifying the NumberConverter but it seems that the sample rate doesn't match and my stream is drifting.

Thanks for the Help!

[pschatzmann]

Integer format conversion is done by the NumberFormatConverterStream or NumberFormatConverterStreamT, but I never tested the 24 bit functionality and I suggest that you prefer 32bits instead.

When I implemented it I was under the assumption that we would need to write 3 bytes. But I think the esp32 expects int32_t values.
Feel free to correct the functionality.

[GuillaumeLeclerc]

Sorry I wasn't clear.

I meant:

[24bit signal][8 bits padding] for a total of 32 bits per sample. (This is to interface with some annoying DSPs).

This is what i ended up with:

        size_t readBytes(uint8_t *data, size_t size) override {
           if (p_stream==nullptr) return 0;
           size_t samples = size / sizeof(TTo);
           TTo *data_target = (TTo *)data;
           TFrom source;
           for (size_t j=0;j<samples;j++){
             source = 0;
             p_stream->readBytes((uint8_t*)&source, sizeof(TFrom));
             data_target[j]= ((int32_t) source) << 8;;
           }
           return size;
        }

But I get very weird results when piping this to I2S. (the zero padding doesn't seem to be at the end of each word. I paste the output of my logic analyzer if that can help.

Thanks a lot!

[pschatzmann]

did you try it in 2 steps

           for (size_t j=0;j<samples;j++){
             source = 0;
             p_stream->readBytes((uint8_t*)&source, sizeof(TFrom));
             TFrom *pt_from = (TFrom *) source;
             data_target[j] = *pt_from;
             data_target[j] = data_target[j] << 8;
           }

[GuillaumeLeclerc]

The Duty cycle and frequency is correct, it's just that there seem to be a random phase shift. Is there something that needs to be done when piping A2DP to I2S to synchronize them maybe ?

[pschatzmann]

What is the datatype of source ?

[pschatzmann]

Are you sure that you do something with the data_target. To me it looks as if you output the input data.

[GuillaumeLeclerc]

In my second example I just do this:

             data_target[j] = -1;
             data_target[j]= data_target[j] << 8;

So I don't think the problem is with the source

[GuillaumeLeclerc]

My gut feeling point me towards an alignment issue between the data and the LRCLK signal.

[pschatzmann]

In this case you can try different I2SFormat values

[GuillaumeLeclerc]

Unfortunately the shift is different at every reboot and I have to follow the I2S format of the DSP I'm using. I think I got something to work with the basic A2DP API though !