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Thread: What is the advantage of using add on audio boards over the inbuilt DAC?

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    What is the advantage of using add on audio boards over the inbuilt DAC?

    So Iíve made this synth thing and am currently using the DAC output on a 3.6 direct into an Amp.
    I am considering adding the PT8211 external DAC, is there any advantage of doing that?
    Also how would one go about conditioning the 3.6 direct DAC output to add say volume control and maybe boost low frequency sounds?

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    Senior Member+ Theremingenieur's Avatar
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    I am considering adding the PT8211 external DAC, is there any advantage of doing that?
    The inbuilt DAC has only a resolution of 12bits which gives a theoretical S/N ratio of 73.6dB. External audio DACs might provide 16bit (PT8211), 24bit(PCM5102A) or even more bits, thus lowering noise (up to -112dB) and distortion (up to -93dB) = higher audio quality.

    More sophisticated audio DACs like the PCM 51xx series have integrated oversampling FIR filters, thus raising the sample rate from 44.1kHz to 352.8kHz, simplifying the analog reconstruction filter design and further increasing the audio quality.
    Also how would one go about conditioning the 3.6 direct DAC output to add say volume control and maybe boost low frequency sounds?
    All this can be done, using either the internal or a better external DAC, using the Teensy audio library with the help of its very simple and convenient GUI design tool.

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Theremingenieur answered your first question quite well. I'll try to get the 2nd part...


    Quote Originally Posted by BrianM View Post
    Also how would one go about conditioning the 3.6 direct DAC output to add say volume control
    Normally you would use an "audio taper" pot to attenuate the DAC's signal, and an opamp as a buffer so you get a strong output rather than a weak one from the resistance of the pot. Pots with a value of 10K to 50K generally work well.


    and maybe boost low frequency sounds?
    Add a biquad filter to your audio system running in the Teensy. On the right-side docs panel, scroll down to setLowShelf() for the function to configure the filter. While you can configure the filter many different ways, generally it's best to avoid gain (amplification) inside the filter. You can get more bass sound by reducing all the higher frequencies, then just turn up the total volume.

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    Thank you very much for the very useful information here.
    So I have ordered a PT8211 and will compare the output with the inbuilt DAC, I will also add a buffer and pot.
    I did try the biquad filter but I didn't get any output from it.
    I set values for LOW, HIGH and BAND (all in one filter component)
    I am not able to find any examples of its use on the web, should i be trying to configure a single filter for LOW, HIGH and BAND pass or should each filter module only contain either LOW, HIGH or BAND?
    Since it has three stages I was assuming I have to configure all three stages?
    Or can I just set one stage as setLowShelf?

    If you are curious as to what I built here is a demo (apologies for the poor sound) I got a better way to record now.
    https://youtu.be/Ok9acd9inn4

  5. #5
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    Ok so I got the filter working, not sure why it didn't output a signal before.
    Difficult to gauge if it is boosting the low frequencies or not. I configured it like so..
    biquad1.setLowShelf(0, 150, 1, 1);
    If I put a few in series will that improve it further?

    I read from the notes about frequencies under 400 Hz, I haven't tried the Chamberlin filter yet, it looks more complicated to setup having three outputs, i guess ill have to mix them all together?

    Basically I am trying to get a good base kick, I have tried the Drum module but I wasn't impressed with that sound. I can get better with SINE and ENVELOPE modules.

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