Samplerates of multiple audio inputs of the Audio Expander

Bethanychm

giuliomoro Yes, IN-2 and IN-3 in the scope screenshot respond to changes in the input sound ,and IN-0 and IN-1 respond but are quieter, the scope shows as blow:

Following your suggestion, I try to swap on the breadboad yellow with brown and blue with green, the results are blow:

IN-0 and IN-1 always respond quieter.

giuliomoro

Can you:

make sure the expander board is firmly pressed against the Bela cape
replace the gain-setting jumper wires on J12 for channels 0 and 1
replace the enabling jumper wires on J10 and J11 for channels 0 and 1

and see if anything improves?

Bethanychm

giuliomoro I checked your 3 points, but there was no improvement.

giuliomoro

Can you set the number of analog inputs to 8 and look at all 8 inputs by moving a the same signal through each of them, one at a time?

Bethanychm

giuliomoro Do you mean that I should check the inputs of analog0-7 one by one?
For example, the code in render() changes to:

int gAudioperAnalog = context->audioFrames/context->analogFrames;
void render(BelaContext* context, void* userData)
{

  for(unsigned int n = 0; n < context->audioFrames; ++n)
  {
  		gPhase += 2.0 * M_PI * gFrequency * gInverseSampleRate;
		if (gPhase >= 2.0 * M_PI)
			gPhase -= 2.0 * M_PI;
  		
  		float out = gAmplitude * sin(gPhase);
  		
	    for (unsigned int ch = 0; ch < context->audioOutChannels; ch++){
	    	audioWrite(context, n, ch, out);
	    }
	    
	  if((n%2) == 0){
	    	input = analogRead(context, n/gAudioFramesPerAnalogFrame, 0);  % analog input channel test from IN 0-7
	  }
    	scope.log(input);

  }
  
}

Is my understanding correct?

Bethanychm

giuliomoro Following my understanding, when I output the same volume of sound, the scope results of each input channel are as follows:

giuliomoro

ok thanks, now concentrate on j10 and j11. Connect pin 7 on j11 to pin 0 on j10, then you should be able to plug sound into input 7 and it should show up on input 0. Does that come in at full amplitude?

Bethanychm

giuliomoro I don't know if I understand you correctly. I plug the mic to pin7 of the caplet (J11-pin0 and J10-pin7 are suspended), and use ananlog(context, n/gAudioFramesPerAnalogFrame,0) to read the sound.

the render() code is:

int gAudioperAnalog = context->audioFrames/context->analogFrames;
void render(BelaContext* context, void* userData)
{

  for(unsigned int n = 0; n < context->audioFrames; ++n)
  {
  		gPhase += 2.0 * M_PI * gFrequency * gInverseSampleRate;
		if (gPhase >= 2.0 * M_PI)
			gPhase -= 2.0 * M_PI;
  		
  		float out = gAmplitude * sin(gPhase);
  		
	    for (unsigned int ch = 0; ch < context->audioOutChannels; ch++){
	    	audioWrite(context, n, ch, out);
	    }
	    
	  if((n%2) == 0){
	    	input = analogRead(context, n/gAudioFramesPerAnalogFrame, 0);  
	  }
    	scope.log(input);

  }
  
}

There is no change:

Is there something wrong with my understanding?

giuliomoro

ok that's interesting, can you remove the capelet and show on the scope:

what you get when plugging 3.3V into analog inputs 0, 1 and 2
what you get when plugging the signal from the microphone into analog input 0, 1 and 2

Make sure you only look at the analog input channel that you are plugging a signal into and not the unconnected ones

Bethanychm

giuliomoro

I plug 3.3V into analog inputs 0, 1 and 2:

int gAudioperAnalog = context->audioFrames/context->analogFrames;
void render(BelaContext* context, void* userData)
{

  for(unsigned int n = 0; n < context->audioFrames; ++n)
  {
	  if((n%gAudioFramesPerAnalogFrame) == 0){
	    	input = analogRead(context, n/gAudioFramesPerAnalogFrame, 0);  % analog input channel from IN 0-2
	  }
    	scope.log(input);

  }
  
}

I plug the signal from the microphone into analog input 0, 1 and 2:

Is there something wrong with my understanding?

giuliomoro

That looks good: the bela cape is working as expected.

Now can you put the capelet back on, remove all the jumpers from it and do the same thing you just did, just plugging the microphones straight into the J10 pins?

Bethanychm

giuliomoro I do the same thing of step2:

Should I try the 3.3V?

giuliomoro

yes

Bethanychm

giuliomoro It looks so wired, so as IN2. Is this the contact issue of caplete and cape?

giuliomoro

Can you show a picture of the boards from the side? I suspect J10's pins are not making proper contact with the socket underneath. Also make sure you run with 8 analog channels enabled when running these tests.

Bethanychm

giuliomoro Yes, I run with 8 analog channels enabled.

Bethanychm

giuliomoro Got!
Here are the new results for 3.3V：

Blow are the mics results with capelet unabled:

Bethanychm

giuliomoro It looks that the two boards are plugged in tightly.

giuliomoro

Oh wait another thing: for this last test, you need to disable the audio expander checkbox in the IDE for the selected channels, otherwise any DC voltage will be filtered digitally.

giuliomoro

Right, so there we see that in https://forum.bela.io/d/3201-samplerates-of-multiple-audio-inputs-of-the-audio-expander/24 we get equal readings from the 3 channels for a 3.3V input when connected directly to the cape, but
then in https://forum.bela.io/d/3201-samplerates-of-multiple-audio-inputs-of-the-audio-expander/32 we get different readings when plugged through J10 on the capelet, even though J10 is a passthrough.

In the last set of pictures, the scale and offset of the channel enabled in each picture is the same, correct? Just double checking.

Do a couple more things for me:

with the capelet connected, plug 3.3V into channel 0 of j10, look at the signal on the scope. Then, place your thumb on the free part of J10, as close as possible to the jumper wire, and the rest of your fingers underneath the BBB. Squeeze them tight while you look at the scope: do you see changes? Does the channel ever reach the expected value of approx 0.8?
Can you show the capelet unplugged from the cape? Are the pins on J10 as long as those on P8 and P9 ?

I see that you are using a rev B cape, where J10 is shorter than P8/P9, so that could be the reason why things don't make great contact.

Bethanychm

giuliomoro Thanks for your double checking, the scale and offset of the channel enabled in each picture is the same.
Then

Yes, I can see the value changing to approx 0.8 when I tightly squeeze them.
J10 looks as long as P8/P9:

So if I need use 4 mics to measure AoA with sample rate of 44.1KHz, this contact problem will be a trouble, right?

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