kopia lustrzana https://github.com/erdewit/HiFiScan
Add section about causality
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README.rst
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README.rst
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@ -7,11 +7,11 @@ The goal of HiFiScan is to help equalize an audio system to get
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the best possible audio quality from it.
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the best possible audio quality from it.
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There are two ways to do this:
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There are two ways to do this:
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1. Manual: The realtime frequency spectrum is displayed and
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1. Manual: The realtime frequency response is displayed and
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the peaks and troughs can be interactively equalized away.
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the peaks and troughs can be interactively equalized away.
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2. Automatic: The frequency response is measured and a correction
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2. Automatic: The frequency response is measured and a correction
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is calculated. This correction is a phase-neutral finite impulse
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is calculated. This correction is by default a phase-neutral finite impulse
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response (FIR) that can be imported into most equalizer programs.
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response (FIR) that can be imported into most equalizer programs.
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The measuring is done by playing a "chirp" sound that sweeps
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The measuring is done by playing a "chirp" sound that sweeps
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@ -96,7 +96,7 @@ and then "Load"):
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.. image:: images/Convolver.png
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.. image:: images/Convolver.png
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We go back to the spectrum measurement and store the uncorrected
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We go back to the spectrum measurement and store the uncorrected
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spectrum with the "Store" button (to compare with later measurements).
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spectrum with the **Store** button (to compare with later measurements).
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More measurements can be stored as well, for example where the microphone
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More measurements can be stored as well, for example where the microphone
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is placed in different locatations, The total average of the stored
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is placed in different locatations, The total average of the stored
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measurements is shown in orange
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measurements is shown in orange
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@ -277,6 +277,31 @@ and in cyan the reshaped spectrum that tries to follow the target curve:
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.. |License| image:: https://img.shields.io/badge/license-BSD-blue.svg
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.. |License| image:: https://img.shields.io/badge/license-BSD-blue.svg
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:alt:
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:alt:
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Causality
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---------
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The default is to create a phase-neutral (aka linear-phase)
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impulse response. It's also possible to create a minimum-phase response.
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Even everything in between is possible. This is done with the **Causality**
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parameter, where 0% is phase-neutral and 100% is minimum-phase.
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Varying the causality smoothly transitions between the extremes:
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.. image:: images/causality-waveform.png
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The latency decreases proportional to the causality.
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At 100% the response becomes zero-latency and purely causal, where only the current
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and later sound samples are used. The pre-echo is eliminated at the price of
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twice the post-echo.
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Note that despite the name of "minimum-phase"
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this setting actually incurs the most phase distortion, which can get severe with
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a steep equalization.
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A good compromise may be a causality of 40%, which reduces the pre-echo
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by about 6 dB while not phase-smearing too much.
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Let your ears be the judge of what sounds best.
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A tool for changing the causality of existing impulse responses (as WAV file)
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is found in "Tools... -> Change IR causality".
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Disclaimer
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Disclaimer
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==========
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==========
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