Teensy 4.1 Audio Shield Real-Time Voice Changer (Military Radio)

[cobalt]

Hi all,

This is my first post and also first project coming back to tinkering after a while (still kind of a rookie at these things). To summarize what I am trying to do, I am looking to create a real-time voice changer using a Teensy 4.1 and Audio Shield. To be specific, I am trying to implement a voice changing effect that would alter a human voice to instead sound like a civil protection officer/metrocop from Half Life 2 as part of a cosplay I am developing.

My physical hardware setup consists of an electret microphone with either a MAX4466 or MAX9814 (experimenting using both) which would act as the line input to the Teensy. Using the audio system design tool and audio library, I've developed a DSP chain to produce the audio effects I am looking for. I would love to receive some feedback on this design and implementation, and if there are other approaches I should look into.

What spurred me to make this post is that I've actually run into a problem that I am struggling to resolve. I have reason to believe it is a grounding issue, but am unsure what to do. I am prototyping by using the teensy fixed onto a breadboard and using short wires to connect everything (besides the headphones). I am powering the teensy via USB and I am powering the mic+9814 with an external power supply. This setup has worked for me with prototyping, however, I don't intend on carrying around a power supply and computer with me

When I've tried to power everything using just the supply, I unfortunately do not hear anything coming from the Teensy...

What mistake am I making in my setup that would cause this issue? Am I causing a ground loop? Am I shorting something?

I've attached a shoddy wiring diagram of my simplified setup (I plan on adding pots and buttons for controls and tuning later). I have also attached my DSP chain and code. If I did something silly, please feel free to laugh at my expense, but also please let me know what that silly thing is!

Best,
Ted

 

[cobalt]

Also, forgot to mention it, but in my final setup I intend to drive a 3W speaker in line with a PAM8403 amplifier!

 

[defragster]

The Audio shield does not use 5V and there is no connection to that pin - silkscreen supplied perhaps just for orientation.

This image showing the active pins from the product page explains why there are no traces leading from the 5V pin on the PCB

 

[cobalt]

My apologies for not being more clear. I have the Teensy and Audio shield connected using stack-able headers. I am powering the Teensy4.1 through the 5V pin, which I assumed would drive the 3.3V output to power the Audio Shield. Is this incorrect?

I did notice in further testing that if I wire the Audio Shield's line in directly to the mic+9814 output (output to L and ground to ground) and not connect it to the shared ground as I have in my diagram, I get some audio out, although the output is drastically reduced. I am doing my best to try and investigate this, but I am also fearful of damaging something. If there are any references or resources I could look at, I would be very grateful.

 

[DD4WH]

You may consider connecting an electret mic directly to the mic input of the audio shield, not the line input, the latter is much less sensitive.

 

[cobalt]

You may consider connecting an electret mic directly to the mic input of the audio shield, not the line input, the latter is much less sensitive.

This is something I was considering but wasn't sure of the tradeoffs. One of the attractive features of using the 9814 was the AGC would help achieve the effect I was looking for.

Also, I seem to have solved my problem. Funny enough, I wired my Line In backwards
I may look into getting an audio ground loop isolator if that is a good practice.

In case anyone was curious, I modified my design a little bit and redesigned my FIR filters. It's all still in the prototyping stage, but I'll provide progress updates if anyone is interested (with more context as to why I did what I did). Also happy to receive C&C, always looking to get better!