Teensy 4.0 Audio Shield - Line In Microphones

Hi Alfred0, sorry to take into the thread,i'm experimenting the use of a cardioid microphone
at one of the 3 inputs of a cs42448 codec board ,ihave a good result with an amp.gain(5.0f)
wired to a mixer.gain(1,3.0),it's a prodipe TT1 mic.
the only trouble is a hum sound but low,surely a lack of impedance adaptation.
 
AntiLoop said:
Hi Alfred0, sorry to take into the thread,i'm experimenting the use of a cardioid microphone
at one of the 3 inputs of a cs42448 codec board ,ihave a good result with an amp.gain(5.0f)
wired to a mixer.gain(1,3.0),it's a prodipe TT1 mic.
the only trouble is a hum sound but low,surely a lack of impedance adaptation.
Click to expand...
Hi AntiLoop, no problem with the thread, is here for learning 😊

I can´t remember properly, but I'm pretty sure that cardioid microphones mostly are dynamic microphones, they use electromagnetism to generate electric pulses that represent the sound that the membrane, which is connected to a magnet, captures, while condenser microphones needs additional power, know as phantom power, so in fact, cardioid microphones should have less problems to be use without any external power or amplifier, and that's why it should be working for you turning up the gain.

At least, that's my theory, also I don't know how cs42448 board works exactly, I suppose that is similar and the ports are line in/out, maybe it has some extra capabilities.

I'm talking from my limited knowledge in sound matter, one of the purposes behind this project was my self-growth in the audio field, trying to understand more deeply some concepts, so take what I said with a grain of salt. What I know is that if you can use an amplifier for your microphone, always is better ahahaha.

For now I'll try to pre-calculate the coefficients of my FIR filter and avoid the use of microphones doing a fixed system, maybe later in the future I'll fight a little bit more with the code and use the information that is being provided here to make it 100% active, but yes, the use of that kind of microphones could be a good trick to avoid external amplifiers.
 
The sensitivity pattern of a microphone is due the the mechanical design mainly. Some condener mics are actually two diaphragms back-to-back that can be switch-selected to add or cancel to provide several different patterns.
 
maybe you can take a look at those systems fitted in comfort headphones or earphones,to eliminate
all noises coming from outside,they certainly use dedicated microphones with a dephasing algorythm
 
AntiLoop said:
maybe you can take a look at those systems fitted in comfort headphones or earphones,to eliminate
all noises coming from outside,they certainly use dedicated microphones with a dephasing algorythm
Click to expand...
Yes, the concept is the same, I've testing with some precalculated coefficients in MatLab using FX-LMS algorithm and seems kind of working, is not clear.

Due to the deadline I had, I can't do more now, so the new deadline is for January, I'll check the library trick that Paul mention previously and see if is possible to make some analysis block capable of doing the FX-LMS efficiently so the system becomes active like those headphones.

I think that could be pretty useful even for other purposes, like making a filter for your inputs to denoise mics, because you can use samples of the noise, so they could be load in a microSD and you can select which type you want to apply.

I really think Teensy board is capable of doing a lot.

When I get better samples from my tests with the actual system I'll share some recording of the results, is really surprising how well it works when it works.
 
Hello, so, just an update, the system is not working as intended yet, but I'm discovering some interesting things.

First of all, I want to know if there's something that I should have in mind when assembling the teensy and audio boards because when I've been testing with the oscilloscope the audio output, I've encounter a frequency at 50Hz, so it's the power grid, and this was confirm after I connected the Teensy to a power bank and the noise disappeared completely.

But also, if I use a laptop connected to the grid, the noise is back so that have me thinking, are all jack ports not isolated from this in every device? Because I don't know at this point if is something natural related to the electronics or I should have more care soldering everything.

This is more for curiosity than necessity, I just want to understand a little more about this; I think isn't relevant for my purposes but you always don't really know .

Right now I'm still testing with some pre-calculated coefficients from MatLab and a fixed physical setup of speakers, and if it works then I'll try to inspect the library and check if is possible to make the system work in real time just as Paul suggested.

Thank you for your time.
 
MarkT said:
Does the laptop power supply have an earth connection?
Click to expand...
Yes, my form teacher doesn't understand also how is happening, because using a standard PC also introduce noise, and the PC is grounded too, it uses typical clover shaped plug, and the laboratory is grounded, so, yes, pretty strange how we're getting noise XD
 
Mains hum is always a problem with low level audio signals - stray mains voltage in the air is at a suprizingly high level, 20V or more isn't unknown. This means the screen for the microphone cable needs to be solid braid for best results. Also using twin-core plus screen cable is typical, with the microphone signal on the core wires (signal and return), and the screen separately connected to ground - the screen shields the core wires from mains signals, and any noise currents in it don't pollute the microphone signal or signal ground. Using simple coax means noise currents on the screen corrupt the microphone signal.

Can you provide a wiring diagram for your current setup ?
 
Hi,alfred,do you still use the mic you posted the photo before?,i think it is bounded to be used with an headphone on a pc,
it has 3 wires plus the ground ,and the pc dispatches the signals,it is good for video conference,but i don't think it is reactive enough
for your noise cancelling.
i just bought one of this,very cheap but i never succeed to get some sound on my TDM line input,i'd better cut the wires
and keep the essential from the mic.
 
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