Teensy 4.1 Audio Adapter Crosstalk

B

bdoan

Well-known member
I seem to be getting crosstalk between Line In and Line Out on the Audio Adapter.
How should the ground terminals in the Line In / Line Out section be wired with respect to other grounds on the 4.1 and the overall system?
If I ground the Line In terminal, the crosstalk goes away (for that channel).
How do I deal with this?
Do I need to have a low impedance buffer (op amp output) driving these inputs?

1733772353486.png

This is the configuration that I am running.
I tested this with different audio interface software and it happens on all of them.
If I just use it for playback, it sounds fine.
But as soon as I introduce the audio inputs, I get distortion in the playback and crosstalk.

This is mission critical .

Please help
 
Last edited:
MarkT said:
I think we need to see how you've wired the audio. Could easily be a ground loop.
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This happens with just the audio adapter piggy backed on the 4.1 with header pins. No external circuitry.

If I short the Lin and Rin, the crosstalk goes away.

The Codec has 29k line input impedance.

Is this just leakage on the adapter pcb?
 
Are you listening to unterminated audio inputs? That's going to be noisy for sure. Line inputs expect to be driven by a low impedance (100 ohms or so is common with opamp circuitry).
 
What will you be plugging into the line inputs? Audio line level devices typically have low output impedance and high input impedance.
 
MarkT said:
What will you be plugging into the line inputs? Audio line level devices typically have low output impedance and high input impedance.
Click to expand...
This is being used on a test fixture where one input may gave a low impedance (<100 ohms) and the other is switched by a mux.
 
MarkT said:
What will you be plugging into the line inputs? Audio line level devices typically have low output impedance and high input impedance.
Click to expand...
I re-tested this bare 4.1 / adapter with 200 ohm terminations on the Lin and Rin
Still see audio out showing up on audio in
 
@bdoan: Without seeing how you have everything interconnected, anything offered would just be a mere guess. You say in an earlier post that it's "just the audio adapter piggy backed on the 4.1 with header pins. No external circuitry.", but that's contradictory with saying that you "see audio out showing up on audio in". How is this being determined?? By what means are you observing the leakage ?? How is anythng & everything (o-scope, multimeter, headphones/speaker, anything else that may be in use, other peripherals, etc. - can't tell since you have not provided anything any more specific) connected ??

Mark J Culross
KD5RXT
 
kd5rxt-mark said:
@bdoan: Without seeing how you have everything interconnected, anything offered would just be a mere guess. You say in an earlier post that it's "just the audio adapter piggy backed on the 4.1 with header pins. No external circuitry.", but that's contradictory with saying that you "see audio out showing up on audio in". How is this being determined?? By what means are you observing the leakage ?? How is anythng & everything (o-scope, multimeter, headphones/speaker, anything else that may be in use, other peripherals, etc. - can't tell since you have not provided anything any more specific) connected ??

Mark J Culross
KD5RXT
Click to expand...
I am using a software interface that sends and receives audio to the (USB) device.

When I send an audio file or even just a tone, I see response coming back from the teensy audio input side.

This should not happen
 
Do you want me (or anyone) to investigate?

I hope you can understand how much guesswork would be involved. You haven't given the code running on Teensy. You haven't said which software you're using on your PC and what specific things you click or type to make it send the tone. Nor have you said which software you use to listen. Unless I missed something, I can't even see if you're running MacOS, Linux or Windows, not to mention which version! At a bare minimum, at least this info and a screenshot showing the exact way you're running these programs.

If you say only that you experience a problem, but you do not give enough info for anyone to reproduce or even observe the problem, helping to solve the problem would require super-human guesswork. I'm not that good. When nobody replies to your question, rather than ask on another thread, consider how you have asked for help. If you give no info to observe or reproduce the problem, odds are slim anyone can help. Nobody replies because your question is lacking essential details.
 
PaulStoffregen said:
Do you want me (or anyone) to investigate?

I hope you can understand how much guesswork would be involved. You haven't given the code running on Teensy. You haven't said which software you're using on your PC and what specific things you click or type to make it send the tone. Nor have you said which software you use to listen. Unless I missed something, I can't even see if you're running MacOS, Linux or Windows, not to mention which version! At a bare minimum, at least this info and a screenshot showing the exact way you're running these programs.

If you say only that you experience a problem, but you do not give enough info for anyone to reproduce or even observe the problem, helping to solve the problem would require super-human guesswork. I'm not that good. When nobody replies to your question, rather than ask on another thread, consider how you have asked for help. If you give no info to observe or reproduce the problem, odds are slim anyone can help. Nobody replies because your question is lacking essential details.
PaulStoffregen said:
Do you want me (or anyone) to investigate?

I hope you can understand how much guesswork would be involved. You haven't given the code running on Teensy. You haven't said which software you're using on your PC and what specific things you click or type to make it send the tone. Nor have you said which software you use to listen. Unless I missed something, I can't even see if you're running MacOS, Linux or Windows, not to mention which version! At a bare minimum, at least this info and a screenshot showing the exact way you're running these programs.

If you say only that you experience a problem, but you do not give enough info for anyone to reproduce or even observe the problem, helping to solve the problem would require super-human guesswork. I'm not that good. When nobody replies to your question, rather than ask on another thread, consider how you have asked for help. If you give no info to observe or reproduce the problem, odds are slim anyone can help. Nobody replies because your question is lacking essential details.
Click to expand...
.
Click to expand...
I will provide a complete breakdown of the test conditions in the morning
Click to expand...

Thanks again for your help
 
PaulStoffregen said:
Do you want me (or anyone) to investigate?

I hope you can understand how much guesswork would be involved. You haven't given the code running on Teensy. You haven't said which software you're using on your PC and what specific things you click or type to make it send the tone. Nor have you said which software you use to listen. Unless I missed something, I can't even see if you're running MacOS, Linux or Windows, not to mention which version! At a bare minimum, at least this info and a screenshot showing the exact way you're running these programs.

If you say only that you experience a problem, but you do not give enough info for anyone to reproduce or even observe the problem, helping to solve the problem would require super-human guesswork. I'm not that good. When nobody replies to your question, rather than ask on another thread, consider how you have asked for help. If you give no info to observe or reproduce the problem, odds are slim anyone can help. Nobody replies because your question is lacking essential details.
Click to expand...
Paul,

After trying multiple software interfaces and 2 different Teensy 4.1 setups, I decided to abandon my scheme of sending USB audio to the Teensy Line Out and simultaneously reading back audio from Line In.

While looking at examples for ToneSweep, I noticed that the setup() condition (AudioMemory() was smaller in my application. Searching AudioMemory on the forum I found that some applications were using values of 24 or higher while I was only using 10.

I changed the value to 127 and my distorted audio issue is solved.

Thank you for your willingness to step in and address this problem and thanks for a great product.
The 4.1 replaces a MPU and USB codec from my previous test fixture designs and makes for a much more efficient and programmable interface.
 
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