QtSimpleOverdrive presentation (QtVST)

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A presentation of the QtSimpleOverdrive VST plugin

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QtSimpleOverdrive presentation (QtVST)

  1. 1. QTSIMPLEOVERDRIVE How it works and how it behaves
  2. 2. Block Diagram <ul><li>The diagram is simple and straigthforward. </li></ul>
  3. 3. QtSimpleOverdrive and oversampling <ul><li>A sine sweep is fed through the plugin, and is displayed as a spectrogram. </li></ul><ul><li>The first spectrogram is the spectrogram of the input. </li></ul><ul><li>The second one is the spectrogram of the distorted output. </li></ul>
  4. 4. Oversampling and spectral content <ul><li>The oversampling has a clear impact on the spectral content. </li></ul><ul><li>A small oversampling will induce a lot of aliasing, even with an efficient low pass over- and undersampling filters </li></ul>
  5. 5. 2x Oversampling <ul><li>The original signal and the distorted content can be selected, but the alias is very important </li></ul>
  6. 6. 8x Oversampling <ul><li>Only the end of the sine sweep content has alias, but at lower than the 2x oversampling. </li></ul>
  7. 7. 32x Oversampling <ul><li>The high end of the sinesweep content shows even less aliasing, although it still has a lot of background noise. </li></ul><ul><li>The alias of the decimation can be seen, but it is low enough in the audible spectrum. </li></ul>
  8. 8. QtSimpleOverdrive and profiling <ul><li>On my laptop with Ubuntu, the test case (2 millions samples for a sin sweep at 96kHz) takes 17s with a 2x oversampling, 20s for a 8x oversampling and finally 54s for an 32x oversampling. On Windows, those timings are respectively s, s and s. </li></ul>
  9. 9. Profil <ul><li>The main culprit is the overdrive algorithm </li></ul><ul><li>The exponential function (the diode transfer function) represents 45%. </li></ul>
  10. 10. Conclusion <ul><li>The 8x oversampling is the best compromise between performance and quality. </li></ul><ul><li>A 32x oversampling can be used for offline rendering. </li></ul><ul><li>Side note: the original sampling frequency should be at least 88.2kHz or 96kHz. </li></ul>

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