Teensy 4.0 Audio Shield only transmitting random noise through headphone jack

[Jforest]

Hey all!

I'm a complete beginner, but even when I've gone to someone I know who's more knowledgeable, he couldn't figure this out either.

I'm trying to create an instrument using Teensy's Audio library. I'm currently in the very basic stages; I'm just trying to get the audio shield to play a note. However, whether I use an example wavetable project, an example WAV player project, or my own project (attached to this post), when I plug my headphones into the headphone jack on the audio shield, all I hear is noise that sounds like a dial-up modem. Obviously that's not intended and I'm completely stumped as to why this is happening. I've double and triple-checked the wiring, and everything seems to be in order, I think.

My project is a very simple copy of the SimpleWavetable example, with a few changes, such as removing the knobs that determine frequency and volume and replacing them with constants. Also, I set up a button connected to an LED that will toggle on / off in accordance with whether or not the note should be playing (on if playing, off if not). As part of my troubleshooting, I even added a statement in loop() to always be playing a C5 note, to no avail. All I seem to be able to get is noise.

Could this be because the Audio Shield is wired to the Teensy via 6in wires as opposed to being soldered directly on top of the Teensy? Or maybe is it the USB connection that's causing the noise? Any help would be greatly appreciated.

Oh, and I can of course provide any pictures / videos / code that is needed to help fix this.

(P.S. - Sorry mods if this is the wrong category or anything, I've never used this forum before)

 

[kd5rxt-mark]

Pictures of your setup would assist others in potentially identifying wiring problems, etc.

Mark J Culross
KD5RXT

 

[Jforest]

Here's what I've got. The more I look into this the more I feel like it's the wires lol.

I can make a diagram of the exact connections if that would help, I know it's a bit hard to tell what's what from the photos.

 

[PaulStoffregen]

Yeah, really difficult to see which wires go where in these photos.

Many people have made this work with similar breadboard wires, so it definitely is possible.

For the sake of troubleshooting, I'd recommend running the guitar synth example. In Arduino IDE, click File > Examples > Audio > Synthesis > Guitar. This program creates a continuous sound output which doesn't depend on the SD card or any other hardware. While you're struggling to just get any good sound output, best to run this sort of simple and known-good example program. While fiddling with the wires, you want 100% certainty the software side is working.

Next, I'd remove the wires on Teensy pins 6, 8, 10, 11, 12, 13, 15. For successful audio output, you only need wires from Teensy pins 7, 18, 19, 20, 21, 23, and of course GND and +3.3V. If you pare it down to only those 8 wires, maybe any mistakes will be easier to see? You should also be able get photos that show the 8 wires more clearly, so we can help look for anything that might not be corrected right. If you shoot more photos, try to get a wider camera angle like the first 2 pictures so we can see both sides of each wire.

One more question about how you're listening. Is it real headphones? There is a common problem where the headphone output has a virtual ground which isn't compatible with direct connection to other grounded equipment while Teensy also has a ground connection via USB or any other cables. Can't see what you're plugging into the headphone jack with any of these photos, so just trying to cover all the known issues. Hopefully it helps?

 

[Jforest]

Alright, that helped! Progress has been made!

I've attached photos of the new setup. Now, while the noise is still happening, if I plug my headphones in only partially - around 75% - I can hear the guitar sounds running from the recommended example. However, any more or less than that results in the noise again.

Here's a video where you can kind of hear what it sounds like, the working guitar is too faint to really hear but you can very clearly hear the noise:

 

[PaulStoffregen]

Connect the GND wire to the GND pin on the audio shield, not the "G" pin next to 3.3V.

 

[Jforest]

Alright, I tried that, fiddled around some more, not much luck though. It was crystal clear for a split second before it went back to noise

 

[Jforest]

Scratch that, I found a solution! I don't know why this works but it does so I'm happy

 

[PaulStoffregen]

Glad you got it working!

Just a guess, but maybe 1 or more of those wires are flaky? It's a rare problem, but we've seen it before a few times as some are poorly made. Might be worthwhile to use your multimeter in ohms mode and measure every wire, especially the ones with sockets using a header pin to get access.

 

[MarkT]

Cheap hook up wires are often AWG 26 or thinnner and CCA rather than copper. Basically they save money by using wire so thin its not compatible with the crimps used, so its not unknown for bad wires to occur (correctly crimped wires are extremely reliable).