Intermitted Static Noise on Teensy 4.0 + Audio Shield in Audio Tutorial

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greg1

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Hello,

I'm just using Teensy (4.0) for the first time and plan to use it for an audio project. I have the Teensy 4.0 and Audio Shield board. Currently I'm just trying to learn how it works so I'm following the audio tutorial here using the Arduino IDE 2 w/ Teensyduino: https://hackaday.io/project/8292-microcontroller-audio-workshop-had-supercon-2015#menu-description, but I'm stuck with an issue and am looking for some tech support.

First, I ran the "Part_1_02_Hardware_test" example in the File>Examples>Audio>Tutorials library and I can hear the beeping in my headphones which confirms the Teensy HW is set up correctly. Next I ran the "Part_1_03_Playing_Music" example which plays one of the four .wav audio clips provided for the tutorial that I uploaded to the SD card (SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV, & SDTEST4.WAV). I am seeing intermittent behavior here when running this code (shown at the bottom). Sometimes it plays the audio file cleanly with no problem, but other times it makes a loud periodic static noise sound that repeats every ~0.25 seconds. I tried changing the code to play a different .WAV file and some work more than others, but the issue can happen with any of the 4 files.

After trying to run this several times I found that sometimes it doesn't play any audio at all and it is unable to read the SD card. It says "Unable to access the SD card" in the serial monitor. For that reason I'm guessing the static audio may be an issue related to reading the SD card? I ran the SD card test in Files>Examples>Audio>HardwareTesting>SdCardTest and the results seem okay:

SD Card Test
------------
SD card is connected :)
Card type is SDHC
File system space is 7939.82 Mbytes.
SD library is able to access the filesystem

Reading SDTEST1.WAV:
Overall speed = 1.35 Mbyte/sec
Worst block time = 0.75 ms
25.75% of audio frame time

Reading SDTEST1.WAV & SDTEST2.WAV:
Overall speed = 1.34 Mbyte/sec
Worst block time = 1.47 ms
50.84% of audio frame time

Reading SDTEST1.WAV & SDTEST2.WAV staggered:
Overall speed = 1.34 Mbyte/sec
Worst block time = 1.16 ms
39.84% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV:
Overall speed = 1.35 Mbyte/sec
Worst block time = 2.23 ms
76.83% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV staggered:
Overall speed = 1.35 Mbyte/sec
Worst block time = 1.53 ms
52.87% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV, SDTEST4.WAV:
Overall speed = 1.35 Mbyte/sec
Worst block time = 2.99 ms
103.02% of audio frame time

Reading SDTEST1.WAV, SDTEST2.WAV, SDTEST3.WAV, SDTEST4.WAV staggered:
Overall speed = 1.35 Mbyte/sec
Worst block time = 1.90 ms
65.38% of audio frame time

Does anybody have any ideas why I may hear a periodic static like that?

A couple extra things to note:
1) I noticed the examples in the tutorial were written for Teensy 3.x so some of the pin assignments (like for SPI and Dout) needed to be changed to match the Teensy 4.0. Could there be anything else in the tutorial that could be giving me problems since I'm using Teensy 4.0?
2) I don't have the audio shield board plugged in directly on top of the Teensy. I have the teensy plugged into a breadboard, and jumper cables (~8") running up to the audio shield board. Could the breadboard and long jumpers be giving me issues with reading from the SD?

Code: 
// Advanced Microcontroller-based Audio Workshop
//
// http://www.pjrc.com/store/audio_tutorial_kit.html
// https://hackaday.io/project/8292-microcontroller-audio-workshop-had-supercon-2015
// 
// Part 1-3: First "Hello World" program, play a music file
//
// WAV files for this and other Tutorials are here:
// http://www.pjrc.com/teensy/td_libs_AudioDataFiles.html

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

AudioPlaySdWav           playSdWav1;
AudioOutputI2S           i2s1;
AudioConnection          patchCord1(playSdWav1, 0, i2s1, 0);
AudioConnection          patchCord2(playSdWav1, 1, i2s1, 1);
AudioControlSGTL5000     sgtl5000_1;

// Use these with the Teensy Audio Shield
#define SDCARD_CS_PIN    10
#define SDCARD_MOSI_PIN  11
#define SDCARD_SCK_PIN   13

// Use these with the Teensy 3.5 & 3.6 SD card
//#define SDCARD_CS_PIN    BUILTIN_SDCARD
//#define SDCARD_MOSI_PIN  11  // not actually used
//#define SDCARD_SCK_PIN   13  // not actually used

// Use these for the SD+Wiz820 or other adaptors
//#define SDCARD_CS_PIN    4
//#define SDCARD_MOSI_PIN  11
//#define SDCARD_SCK_PIN   13


void setup() {
  Serial.begin(9600);
  AudioMemory(8);
  sgtl5000_1.enable();
  sgtl5000_1.volume(0.5);
  SPI.setMOSI(SDCARD_MOSI_PIN);
  SPI.setSCK(SDCARD_SCK_PIN);
  if (!(SD.begin(SDCARD_CS_PIN))) {
    while (1) {
      Serial.println("Unable to access the SD card");
      delay(500);
    }
  }
  delay(1000);
}

void loop() {
  if (playSdWav1.isPlaying() == false) {
    Serial.println("Start playing");
    playSdWav1.play("SDTEST2.WAV");
    delay(10); // wait for library to parse WAV info
  }
  // do nothing while playing...
}
 
greg1 said:
I don't have the audio shield board plugged in directly on top of the Teensy. I have the teensy plugged into a breadboard, and jumper cables (~8") running up to the audio shield board. Could the breadboard and long jumpers be giving me issues with reading from the SD?
Click to expand...
Yes, the long wires will likely be the cause of your problems, but not for SD card reading, but for the I2S communication between T4 & audio board.

Solder the audio board to the T4 or use pin headers as short as possible.

Problems can even occur with wire lengths as short as 2 cms between T4 and Teensy audio board.
 
Thanks for the comment. I'll have to put some female headers on the audio board so it can plug directly into the Teensy.

I also noticed that when I mix two audio signals, it never works and always produces the static noise, unlike the single audio which sometimes works. Maybe that cases stresses the I2S even more than the single channel case?
 
Thanks jensa. The issue you saw line up pretty closely with what I'm seeing. I was using a UHS-1 card. It's the exact same model shown in the tutorial so I assumed it wouldn't be an SD card related issue. I'm ordering a UHS-3 card and I'll try it out. Thanks!
 
Might be worth trying with several cards like i did? I was surprised at how different the output I got was. I'm pretty sure that I tried a Sandisk Ultra some years ago and that did actually play back multiple sounds? Might be that they've reduced the quality on these cards over the years then?
 
I got a SanDisk Extreme UHS-3 card and unfortunately I still get the harsh noise issue when trying to mix 2 audio files. Playback for a single file is still fine. I'm next going to try not using long (~8") jumper cables between the teensy and audio board per DD4WH's recommendation. For that I have to remove the header pins from the audio board and solder new ones.
 
The issue is now fixed after I soldered female headers on my Audio Shield board and plugged it directly into the Teensy. Thanks for the help.
 
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