Do tube amps smooth out digital signals?

  • Mathematics laws mean there can only be one solution, one resulting wave, that runs through those points

    Once the 20khz filter has been applied ;)
    How does the curve look like before the filter is applied ? There is a step between recorded samples and analog audio coming out of the converter.

  • Once the 20khz filter has been applied
    How does the curve look like before the filter is applied ? There is a step between recorded samples and analog audio coming out of the converter.

    Actually, it's whatever the frequency the Nyqvist law dictates with regard to the sample rate, 22.05 kHz in the case of a 44.1 kHz sample rate, the Kemper default. The filter is applied before sampling, by the way, so the "curve" looks like whatever audio is going in to the converter. The step between AD and DA conversion is binary only; there is no curve, the wave exists only as digital values at the sample points, the shape of the wave being determined once the sampling points are interpreted by the DA converter. I'm not quite sure what you are trying to get at or don't understand?

    Sure, they are all sine wave, just of very high frequency... which is then filtered by the 20khz filter.

    True, except as I stated above, the filtering frequency is determined by the law of Nyqvist with regards to the sample rate, and is performed beforedigitisation.

    And i see nowhere in the vid (i stopped when he began talking about bit depth) the curve before 20khz filtering.

    Yes, you did. It is shown on the lefthand oscilloscope.

  • The filter is applied before sampling

    We are talking about the digital to analog, don't complicate things !


    Your point, if i understand you correctly, was that the stairsteps doesn't exist.


    My point is that they DO exist.


    The decoding steps are like these :
    1) PCM audio (sample values) -> 2) "stairsteps" like analog signal -> 3) audio at the output of the DAC.


    Between step 2 and 3 there is an audio filter, at 20khz in the case of 44.1khz sampling rate, which transform a "stairsteps" like signal to the audio output we are getting. This filter doesn't do anything else than removing the high frequency content above Nyquist frequency, which is what make the signal look stairsteps like, and that a human cannot hear even if there was no filtering, which was my initial point.

    Yes, you did. It is shown on the lefthand oscilloscope.

    The lefthand scope shows what is going out of the DAC after the 20khz filter, not before.

  • Dude, you are so mistaken, I don’t know where to begin, so I won’t. Please, watch the whole video and stop using Wikipedia as your AD/DA guru. :)

  • Various links that attest that the analog signal before low pass filtering is stairsteps like


    http://www.indiana.edu/~emusic…_audio/chapter5_dac.shtml


    Smoothing filter: Because the output of a DAC creates a stairstep wave (as in the sampling rate diagram of the previous module) instead of a smoother analog one, a smoothing (lowpass) filter tuned to the sampling rate acts to reduce the discontinuity of those steps and the unwanted frequencies they can produce. Although the DAC is operating above twice the Nyquist frequency, in high-resolution audio, the sharp discontinuities of the stairstep wave cause high harmonic frequencies that can alias into the audio range, therefore the smoothing filter is required. What emerges from the final output is a more continuous analog voltage that can be connected to an amplification chain (mixer, amp, speakers, etc.).



    https://en.wikipedia.org/wiki/Digital-to-analog_converter


    Piecewise constant output of a conventional DAC lacking a reconstruction filter. In a practical DAC, a filter or the finite bandwidth of the device smooths out the step response into a continuous curve.



    http://www-inst.eecs.berkeley.edu/~ee247/fa05/lectures/L17_2_f05.pdf



    DAC Reconstruction Filter

    Need for and
    requirements depend
    on application

    Tasks:

    Correct for sinc distortion

    Remove “aliases”
    (stair
    -
    case
    approximation)


    http://www.dspguide.com/CH3.PDF



    https://ibb.co/b1SmzK



    https://books.google.fr/books?…=stairsteps%20dac&f=false


    The stairsteps appearance can be reduced or eliminated by low pass-filtering the DAC output signal before passing it on to the controller


    https://books.google.fr/books?…=stairsteps%20dac&f=false


    There are actually two entirely separately arising spectral impurities (frequency components that were not present in the original analog signal) in the output of a DAC having a zero order hold :quantization noise and stairsteps noise. Even if the number of bits of quantization is very large, leading to effectively no quantization error, there will still be a very large stairstep component in the DAC output which was not in the original analog signal. Referring to a sine wave, for example, the amplitude of the stairstep component is large when the number of samples per cycle of the sine wave is low, and decreases as the number of samples per cycle increases.
    Fortunately, the frequencies comprising the stairstep component all lie above the Nyquist limit and can be filtered out using a lowpass reconstruction filter designed especially for zero-order reconstruction