Quick guide to dynamic microphone connections

veryape999

Hi, I am new to Bela and Pure Data as well. I'm struggling to find resources to connect a dynamic microphone to Bela. Is there anyone to give a quick guidance? I would appreciate it.

giuliomoro

What microphone is it and have you got an external preamplifier?

veryape999

It is a dynamic microphone Shure SM58

giuliomoro

if you have no external preamplifier, connect it as follows:

the + (hot) terminal of the XLR to Bela's L input
the - (cold) terminal of the XLR to Bela's R input
the GND terminal of the XLR to Bela's GND

Then in the software you should subtract the left input from the right input, e.g.: in C++

float micIn = audioRead(context, n, 0) - audioRead(context, n, 1);

or in Pd:

[adc~ 1]
|
|  [adc~ 2]
|  |
[-~ ]
| <<< here you have the mic signal

If you need to boost or attenuate the signal, you can use Bela's input gain setting in the IDE (needs to restart the program for it to be applied), making sure to set it to the same value for both L and R channels.

lstrauss

Hi!

I'm also working with Bela & a SM57 dynamic mic. For clarification, could I use this connection chain?

SM57 XLR --> [adapters taking mono XLR to stereo minijack]* --> Bela audio adapter cable --> Bela audio in
Then subtract the left input from the right input in software.

*Here are the links to the adapter cables from XLR to minijack. If I understand correctly, these need to convert the mono XLR signal into a stereo signal for Bela:
https://www.thomann.de/intl/neutrik_na3ff_xlr_adapter.htm?shp=eyJjb3VudHJ5Ijoic2UiLCJjdXJyZW5jeSI6OSwibGFuZ3VhZ2UiOjJ9&reload=1&glp=1&gad_source=1&gclid=Cj0KCQiAyeWrBhDDARIsAGP1mWR3KsV91p7GRFKnd9C4n98eBB2GuKOcoVmm-VL5mCEGu4dXHnCY6k0aApTvEALw_wcB
and:
https://rode.com/en/accessories/adaptors-cables/vxlr#section-related-products

To my understanding, this is what the Bela audio adapter cables do already:

giuliomoro the + (hot) terminal of the XLR to Bela's L input
the - (cold) terminal of the XLR to Bela's R input
the GND terminal of the XLR to Bela's GND

So I can use the adapter cable and not need to connect the XLR to Molex wires directly?

And for future reference if we want two mic input channels (like actual stereo) we could use an adapter like this:

https://www.thomann.de/intl/cordial_cfy3wff_yaudiokabel.htm?shp=eyJjb3VudHJ5Ijoic2UiLCJjdXJyZW5jeSI6OSwibGFuZ3VhZ2UiOjJ9&reload=1&glp=1&gad_source=1&gclid=Cj0KCQiAyeWrBhDDARIsAGP1mWRZ05-OxiTolbb-Asy2LCsp1m7nK3-qVw3y1_p1tUM6-Es9YCEK_EAaAtN-EALw_wcB

In which case, we wouldn't do this software step?

giuliomoro Then in the software you should subtract the left input from the right input

Thanks!

giuliomoro

lstrauss So I can use the adapter cable and not need to connect the XLR to Molex wires directly?

That seems right, yes.

lstrauss And for future reference if we want two mic input channels (like actual stereo) we could use an adapter like this:
In which case, we wouldn't do this software step?

You can use that cable. Keep in mind that in that cable each microphone would be bringing only one of its signals to Bela's inputs so there is no way of applying the same "pseudo-balancing" trick we used above, so you'll use the left and input signal separately, one for each microphone.