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Thread: Teensy's low pass frequency response

  1. #1
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    Teensy's low pass frequency response

    Hi guys!

    I'm building a guitar pedal with a Teensy 4.0 and an Audio Shield and I came to realize that, even without any processing block, it acts like a low pass. This introduces a lot of mud into the guitar sound and distorts low frequencies.

    This is the audio spectrum obtained in Audacity from a song I recorded using the Teensy without any processing block.
    Click image for larger version. 

Name:	Screenshot 2022-11-30 140938.png 
Views:	10 
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ID:	29833
    Is there anything I can do to correct this? Is this normal?

  2. #2
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    Quote Originally Posted by Sequoia101 View Post
    Hi guys!

    I'm building a guitar pedal with a Teensy 4.0 and an Audio Shield and I came to realize that, even without any processing block, it acts like a low pass. This introduces a lot of mud into the guitar sound and distorts low frequencies.

    This is the audio spectrum obtained in Audacity from a song I recorded using the Teensy without any processing block.
    Click image for larger version. 

Name:	Screenshot 2022-11-30 140938.png 
Views:	10 
Size:	90.7 KB 
ID:	29833
    Is there anything I can do to correct this? Is this normal?
    Your song is probably not very similar to https://en.wikipedia.org/wiki/White_noise Only in this case you would see a more linear spectrum.

  3. #3
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    If you search the forum, you can find audio-shield spectrum plots.

  4. #4
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    Quote Originally Posted by Mcu32 View Post
    Your song is probably not very similar to https://en.wikipedia.org/wiki/White_noise Only in this case you would see a more linear spectrum.
    Well any song will produce a spectrum like this one. Whenever I play my 6th string (the lowest one), the sound heavily distorts.

  5. #5
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    Quote Originally Posted by Sequoia101 View Post
    Well any song will produce a spectrum like this one. Whenever I play my 6th string (the lowest one), the sound heavily distorts.
    ?? Any song you record is not white noise. Not sure what you're trying to say. A recorded song will *never* show a linear spectrum.
    Distortions may caused by too high input level?

  6. #6
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    Also, keep in mind that the shield is consumer quality. But it's quite ok.

  7. #7
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    Quote Originally Posted by Mcu32 View Post
    ?? Any song you record is not white noise. Not sure what you're trying to say. A recorded song will *never* show a linear spectrum.
    Distortions may caused by too high input level?
    Right, but it will rarely show this kind of low pass response. If I reduce the level of input the high frequencies become barely audible. I have no way to test it with white noise now but I will when I can.

  8. #8
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    Well, the shield is not as bad as your plot shows. There is something wrong. But you simply can't judge that from a song.
    Do you use the linear input? (not mic)


    The user blackadr made a quite good board. I've used it (well, a modification by myself)

    http://blackaddr.com/products/

  9. #9
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    Here's an article about self-noise : http://openaudio.blogspot.com/2017/0...elf-noise.html

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