[Ardour-Users] export format profile

[Gunter Königsmann]

Imagine you have an audio hardware that can only output 8-bit samples
but that has a samplerate of 1 million samples per second.

That means you would only be able to output 256 separate values
(0...255). But if you really wanted to output the value 128.5 you could
nearly do so by alternating between outputting an 128 and an 129.

The easiest way to archive this result is to add a small signal of the
height +/-0.5 values to your audio data. Ardour now allows you to choose
what shape this signal has:

  * None: The additional signal is zero. If you want to output an an
    128.5 your output signal is rounded, presumably to 129.
  * Rectangular: The additional signal alternates between 2 values.
    Which means your audio signal's resolution is effectively increased
    by only 0.5 bits at the cost of introducing an extremely low buzzing
    that using today's sample rates always lies outside the audible range.
  * Triangular: The additional signal is of a triangular shape. Which
    means the audio resolution is increased more than with setting
    "rectangular". But the additional signal that allows to do this is
    in the audible frequency range and is at a single frequency so if
    you krank up the volume of your stereo while the input signal's
    amplitude is extremely low you might be able to hear the triangular
    signal.
  * Shaped Noise: The additional signal is noise with a certain
    frequency spectrum. Which means the spectrum of the 0,5 bit high
    medium error the dithering introduces during improving the
    resolution is spread over a wild range of frequencies. Even if you
    krank up your stereo enough to be able to hear a signal of the hight
    of only 0.5 samples in this case what you'll hear is a low-amplitude
    noise like the one the stereo will produce, anyway.

Personally I would choose "none" or "shaped noise".

Kind regards,

   Gunter.

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