Audio Shield line-out question

[robedney]

Using the Teensy pass through sketch example to simplify, I am adjusting the line-out volume from the Audio Shield to an amp. I'm using the sgtl5000_1.lineOutLevel(left,right) command but the range of control, although it works, seems limited (for example I cannot approach zero output). My understanding is that the parameters for left/right are 13 through 31. Please, what am I doing wrong???

/*
 * A simple hardware test which receives audio from the audio shield
 * Line-In pins and send it to the Line-Out pins and headphone jack.
 *
 * This example code is in the public domain.
 */

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

// GUItool: begin automatically generated code
AudioInputI2S            i2s1;           //xy=200,69
AudioOutputI2S           i2s2;           //xy=365,94
AudioConnection          patchCord1(i2s1, 0, i2s2, 0);
AudioConnection          patchCord2(i2s1, 1, i2s2, 1);
AudioControlSGTL5000     sgtl5000_1;     //xy=302,184
// GUItool: end automatically generated code


const int myInput = AUDIO_INPUT_LINEIN;
//const int myInput = AUDIO_INPUT_MIC;


void setup() {
  // Audio connections require memory to work.  For more
  // detailed information, see the MemoryAndCpuUsage example
  AudioMemory(12);

  // Enable the audio shield, select input, and enable output
  sgtl5000_1.enable();
  sgtl5000_1.inputSelect(myInput);
  sgtl5000_1.volume(0.5);
   sgtl5000_1.lineOutLevel(31, 31);
}

elapsedMillis volmsec=0;

void loop() {
  // every 50 ms, adjust the volume
  if (volmsec > 50) {
    float vol = analogRead(15);
    vol = vol / 1023.0;
    //audioShield.volume(vol); // <-- uncomment if you have the optional
    volmsec = 0;               //     volume pot on your audio shield
  }
  //lineOutLevel(22, 22);
}

 

[kd5rxt-mark]

Think of the function that you are currently calling as a "gain" setting (determines the maximum possible output). Actual volume should be controlled with the sgtl5000_1.volume() function (see screen capture), which takes a parameter ranging between 0.0 & 1.0. Take note of the "0.8 maximimum without distortion" warning on the level value.

Hope that helps . . .

Mark J Culross

 

[robedney]

Thanks for that --however there's a limitation to the volume(level) control in that is effects both left and right channels equally. I'd like control over what I feed to the amp separately per channel. the other issue is that -- from what I've read and tested -- the volume(level) control only effects the headphone jack on the shield and not the audio out pins. More thoughts??? Am I wrong????

 

[kd5rxt-mark]

Doh, sorry. I skipped right over the fact that volume() affects only the headphones. You are 100% correct. So, my next suggestion (hopefully, after a little more thought than the last time) would be to possibly include something like a mixer in each of the L & R signal paths feeding the L & R channels of your I2S output. You would still use the lineOutLevel() as the primary gain setting, but use the individual mixer setting to adjust the fine control level of the L & R signals indepenently (even all the way to 0-level).

Hope that helps (better than the last) . . .

Mark J Culross
KD5RXT

 

[TomChiron]

dacVolume in the SGTL5000 control object is another option to control the overall volume before output.

 

[PaulStoffregen]

The sgtl5000 lineOutLevel() functions are meant to adjust the overall signal level. They're not meant to be a volume control which goes down to zero.