Audio input

Electrumpet

What is a few centimeters? The objective is to have the Bela very close actually. The microphone will be close to P1.1. I might be able to do it with headers bend in such a way that a super small breakout board with the microphone can be connected to a PCB board directly without wires.

Would you have a recommendation for the microphone considering signal quality? What I think I need for the project is:

Able to handle large SPL levels (in the lead pipe of a trumpet. I don't know what the maximum is in the lead pipe, but 120-130 dB might be necessary).
Preferably directional. I want to incorporate it in the wall of the leadpipe or mouthpiece receiver and it should not pick up surrounding sound (that is also packing of course).
Big signal/noise difference. Able to handle the large differences in sound between normal trumpet sounds and clicks and such.
Very small form factor. A 4x3 mm package for example. If the microphone has some height away from the PCB board, that might actually help for the construction, although I also see examples where the sensor is exposed as a hole on the backside of the breakout. I aim to have such a whole/the microphone as part of the sidewall of the trumpet lead pipe/mouthpiece receiver. It has to be small so as to minimize the impact on the acoustic sound (an issue I have with my current setup).

Thanks for thinking with me.

Best, Hans.

giuliomoro

Electrumpet The microphone will be close to P1.1. I might be able to do it with headers bend in such a way that a super small breakout board with the microphone can be connected to a PCB board directly without wires.

Sounds close enough for I2S. On the Bela side, if you use an I2S microphone you'll need as a preparatory step to apply this patch to /opt/bb.org-overlays and then do make && make install and reboot:

diff --git a/src/arm/BB-BELA-00A1.dts b/src/arm/BB-BELA-00A1.dts
index 305e2c3..535f986 100644
--- a/src/arm/BB-BELA-00A1.dts
+++ b/src/arm/BB-BELA-00A1.dts
@@ -20,6 +20,7 @@
                target = <&ocp>;
                __overlay__ {
                        P2_26_pinmux { status = "disabled"; };
+                       P2_28_pinmux { status = "disabled"; };
                        P2_30_pinmux { status = "disabled"; };
                        P2_32_pinmux { status = "disabled"; };
                        P2_34_pinmux { status = "disabled"; };
@@ -74,6 +75,7 @@
                                         * runtime and manage the conflict with CTAG pins */
                                        /* For AXR0 on P9.30 we do something similar so that it can be used
                                         * for SPI */
+                                       0x1a8 0x28 /* mcasp0_axr1,              P2_28 | MODE0 | INPUT_NOPUPD */
                                >;
                        };

Wire your microphone with the LRCLK/WCLK from P1.33, the BCLK from P1.36, and put the data line into P2.28.
Then you should run your project with the added command line option --board BelaMiniMultiI2s and you should have 4 inputs and 4 outputs in your project, with the Bela inputs and outputs on channels 0 and 2 and your microphone input on channel 1 or 3. Remaining channels are unused.

I don't have specific microphone recommendations, though, unfortunately, neither I2S or analog output.

Electrumpet

Wow. Thanks for the quick and comprehensive reply. I'll first work on getting the microphone working and look into microphone specifications later.

Just a few additional questions:

I only need the one microphone input and no output, nor other inputs. Can anything be further optimised for that?
Does this patch influence any of the other inputs? I use the analog inputs (5 of them), I2C (both ports) and possibly SPI.

Thanks, Hans.

giuliomoro

Electrumpet inputs. Can anything be further optimised for that?

If you remove 3 from outSerializers in core/I2c_*MultiI2*.cpp then you can have only two outputs and save maybe less than half percent of cpu time.

Electrumpet Does this patch influence any of the other inputs?

Electrumpet

thanks!

kaos

Hi,

Do these instructions still work for the Bela GEM Multi? I have some INMP441 I2S MEMS mic modules I want to connect to the bela GEM multi, Ideally on a shield I can stack on top of the headers.

In the end I want to do 2 [adc~] in pure data and readout the mic.

From what I understand this is probably not gonna work as the I2S is giving a digital signal?
So how does this wqork. Am I defining extra ADCs somewhere?
How far of a solution am I? I'm usinmg these cheap modules (or I would like to do so) resulting in a stereo mic input for my bela GEM.

giuliomoro

You should be able to do something similar with the Gem Stereo by using the I2S lines that would be normally used by the Multi:

These are the available inSerializers:

{4, 0x3},  P1.2,
{5, 0x3}, P1.35

So, in core/I2c_Codec.cpp, find this block:

#if defined(IS_AM62_SK)
        mcaspConfig.params.inSerializers = {{3, 0x3}};
        mcaspConfig.params.outSerializers = {{2, 0x3}};
#elif defined(IS_AM62_BP)
        mcaspConfig.params.inSerializers = {{2, 0x3}};
        mcaspConfig.params.outSerializers = {{1, 0x3}};
#elif defined(IS_AM62_PB2)
#ifdef BELA_PB2_UPGRADE_REVA_NOREWORK
        // data lines are swapped, oops!
        mcaspConfig.params.inSerializers = {{0, 0x3}};
        mcaspConfig.params.outSerializers = {{1, 0x3}};
#else
        mcaspConfig.params.inSerializers = {{1, 0x3}}; // CHANGE THIS
        mcaspConfig.params.outSerializers = {{0, 0x3}};
#endif
#else
        mcaspConfig.params.inSerializers = {{0, 0x3}};
        mcaspConfig.params.outSerializers = {{2, 0x3}};
#endif

and replace the line marked CHANGE THIS above with this:

mcaspConfig.params.inSerializers = {{4, 0x3}}; // P1.2

Use P1.2 for I2S data input, then take WCLK from P2.10 and the BCLK from P2.19.

If instead you want to use these microphones alongside the built-in codec's inputs, you'd need to modify core/ I2c_MultiI2sCodec.cpp and core/board_detect.cpp as follows:

diff --git a/core/I2c_MultiI2sCodec.cpp b/core/I2c_MultiI2sCodec.cpp
index 57a97fa2..85fdbbb4 100644
--- a/core/I2c_MultiI2sCodec.cpp
+++ b/core/I2c_MultiI2sCodec.cpp
@@ -11,12 +11,11 @@ I2c_MultiI2sCodec::I2c_MultiI2sCodec(int i2cBus, int i2cAddress, CodecType type,
 	setParameters(p);
 	I2c_Codec::getMcaspConfig();
 	mcaspConfig.params.inSerializers = {
-		{0, 0x3},
-		{1, 0x3}
+		{1, 0x3}, // on-board codec
+		{4, 0x3}, // P1.2
 	};
 	mcaspConfig.params.outSerializers = {
-		{2, 0x3},
-		{3, 0x3}
+		{0, 0x3}, // on-board codec
 	};
 }

diff --git a/core/board_detect.cpp b/core/board_detect.cpp
index 52856fdf..d6612282 100644
--- a/core/board_detect.cpp
+++ b/core/board_detect.cpp
@@ -273,7 +273,7 @@ bool Bela_checkHwCompatibility(BelaHw userHw, BelaHw detectedHw)
 		return true;
 	else if (userHw == BelaHw_BelaMultiTdm && Bela_hwContains(detectedHw, BelaCape))
 		return true;
-	else if (userHw == BelaHw_BelaMiniMultiI2s && Bela_hwContains(detectedHw, BelaMiniCape))
+	else if (userHw == BelaHw_BelaMiniMultiI2s)
 		return true;
 	else if (userHw == BelaHw_BelaMini && Bela_hwContains(detectedHw, BelaMiniCape))
 		return true;

and run with --board=BelaMiniMultiI2s

All of the above untested and unsupported.

kaos

giuliomoro but I am using the bela multi, So I'm guessing it's not a good idea to do the above?

giuliomoro

Then it won't work there: the codecs assume a data format that's not I2S, otherwise we couldn't fit all the channels on there. However, if you switch to PDM microphones (instead of I2S), you can connect up to 8 of them to inputs 2 through 9 with the correct software flags.

kaos

Ok, that 's clear this adafruit PDM mic would be a good candidate?

giuliomoro

yes that looks fine, I think that's the one we used for testing.

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