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Thread: Audio Board Line In Noise

  1. #1
    Junior Member
    Join Date
    Sep 2014
    Posts
    17

    Audio Board Line In Noise

    I have a Teensy 3.2 soldered on Top of Teensy Audio Board with SGTL5000.
    Line In connection is soldered to ground.
    Output is USB Audio, Clock of Teensy is 96 MHz
    USB 5V is disconnected, Power is 9V battery with 5V linear regulator

    Following sketch i am using:

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



    // GUItool: begin automatically generated code
    AudioInputI2S i2s1; //xy=236,337
    AudioOutputUSB usb2; //xy=518,247
    AudioOutputI2S i2s2; //xy=518,311

    AudioConnection patchCord1(i2s1, 0, usb2, 0);
    AudioConnection patchCord2(i2s1, 0, i2s2, 0);
    AudioConnection patchCord3(i2s1, 1, usb2, 1);
    AudioConnection patchCord4(i2s1, 1, i2s2, 1);

    AudioControlSGTL5000 sgtl5000_1; //xy=376,109
    // GUItool: end automatically generated code


    void setup() {

    AudioMemory(10);

    sgtl5000_1.enable();
    sgtl5000_1.inputSelect(AUDIO_INPUT_LINEIN);

    sgtl5000_1.volume(0.8); // headphone volume
    sgtl5000_1.adcHighPassFilterDisable(); // reduction of noise floor in some cases

    sgtl5000_1.lineInLevel(0);
    }

    void loop() {
    while(1);
    }

    I record the Audio Ouput with Adobe Audition and i get following graph.
    I have amplified the audio a little, so that it can be seen. It always can be heared direct when connecting a headphone to the teensy audio board.

    Click image for larger version. 

Name:	Teensy Audio 0 dB Line In.png 
Views:	48 
Size:	37.4 KB 
ID:	11387


    I have recorded the audio, but i do not know how to submit this mp3 file.

    I made several tests with the audio board. USB Audio ouput from PC to Teensy generated absolute no noise. Line In always has a lot of noise, even when setting Line In to 0 dB.

    Question: Is this normal behavior of the Audio board and if Yes, which Audio Board could be a replacement with much better Signal to Noise ratio of the Line Input.

    Thanks in advance
    Last edited by otti123; 08-27-2017 at 09:09 AM.

  2. #2
    Member Revalogics's Avatar
    Join Date
    Dec 2016
    Location
    Philippines
    Posts
    78
    Hi, you can just link your mp3 file here from somewhere you uploaded it (like Google Drive, Facebook, etc., click the BB code below in posting permissions).

    Try increasing AudioMemory if that makes any difference.

    Personally, I can't buy an Audio board, so I made one using UDA1345TS.
    I first found this chip in a DSP board (Audio effects board) in an audio mixer.
    I have some spare board, so I decided to remove the DSP parts from the PCB, and leave the CODEC and its extra parts.
    The CODEC is configured as follows:
    MC1 - HIGH
    MC2 - HIGH
    MP1 - LOW
    MP2 - LOW
    MP3 - LOW
    MP4 - HIGH
    MP5 - HIGH

    It works without issues with the Audio Library using I2S objects (no SGTL5000 objects though).
    I got impressive performance with this chip (input noise floor at less than -85 dBFS, outputs can drive headphones, powered at 3.3V).
    The input is line level though.
    If you want, I will create a PCB layout and link it back to you.
    Also note that I don't sell this PCBs because I homebrew my own PCBs. Maybe you can DIY or send them to Osh Park or something.
    The chip also has very fine-pitched pins (0.65mm) so manual soldering tends to be difficult.

    Revalogics
    Last edited by Revalogics; 08-27-2017 at 04:19 PM.

  3. #3
    Quote Originally Posted by Revalogics View Post

    It works without issues with the Audio Library using I2S objects (no SGTL5000 objects though).
    I got impressive performance with this chip (input noise floor at less than -85 dBFS, outputs can drive headphones, powered at 3.3V).
    The input is line level though.
    If you want, I will create a PCB layout and link it back to you.
    Also note that I don't sell this PCBs because I homebrew my own PCBs. Maybe you can DIY or send them to Osh Park or something.
    The chip also has very fine-pitched pins (0.65mm) so manual soldering tends to be difficult.

    Revalogics
    Dear Revalogics,
    I will be happy to look at your PCB design and other things you have that will help me to build my own audio board...
    I've got the same high noises while using the Teensy Audio Adapter...
    Thanks in advance
    Alon

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