Fraction miminum frequency

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Fraction miminum frequency

Permanent link to this post Posted by Piotr Grochowski » Fri Jun 23, 2017 12:58 pm

The minimum frequency must be an integer

I don't like it. It doesn't allow me to get 27.5.

Second: Please allow nearest neighbor resizing of sounds. A maximum frequency sound becomes a square wave as frequency is raised. Perhaps a "Nearest neighbor (no aliasing)" that mirrors the same option for square wave, but make sure integer upsamplings are exact.

Please allow selecting a different algorithm for downsampling. A good simple one would be box sampling - pick a few samples and average them. This should somewhat remedy the issue of high frequency aliasing with downsampling using nearest neighbor and bilinear.
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Re: Fraction miminum frequency

Permanent link to this post Posted by Piotr Grochowski » Sun Jun 25, 2017 8:37 am

In addition to nearest neighbor, also add bilinear and cosine interpolation for upsampling. Cosine is one of the interpolation options in Graphic mode of Equalization.
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Re: Fraction miminum frequency

Permanent link to this post Posted by steve » Mon Jun 26, 2017 1:36 pm

You can generate fractional frequencies using the Nyquist Prompt effect http://manual.audacityteam.org/man/nyquist_prompt.html

The simplest way to do this, for example a 27.52 Hz sine wave is:

1) Select a region of an audio track (mono or stereo) that is the length (duration) that you require.
2) Type the following code into the Nyquist Prompt effect and apply (click the OK button)
Code: Select all
(hzosc 27.52)
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Re: Fraction miminum frequency

Permanent link to this post Posted by steve » Mon Jun 26, 2017 1:45 pm

Audacity provides 4 resampling settings which can be selected in "Preferences >Quality > High-quality Sample Rate Converter".
For detailed specifications of the resampling algorithms, please refer to SoX documentation (Audacity uses the soxr resampling library).

Two additional algorithms are available via the Nyquist Prompt. See here for details:
FORCE-SRATE http://www.audacity-forum.de/download/e ... l#index227
RESAMPLE http://www.audacity-forum.de/download/e ... l#index249
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Re: Fraction miminum frequency

Permanent link to this post Posted by Piotr Grochowski » Tue Jun 27, 2017 5:38 am

I'm talking about minimum frequency for spectrograms, not generating a frequency or resampling.

Image
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Re: Fraction miminum frequency

Permanent link to this post Posted by steve » Tue Jun 27, 2017 7:45 am

Piotr Grochowski wrote:I'm talking about minimum frequency for spectrograms

What does it matter? Why not just set the minimum frequency to 20, 25 or 27 Hz? That setting has no affect on the sound. It only affects the visual display in Spectrogram track view (http://manual.audacityteam.org/man/spec ... _view.html)
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Re: Fraction miminum frequency

Permanent link to this post Posted by Piotr Grochowski » Tue Jun 27, 2017 9:50 am

If I print-screen the logarithmic spectrogram with minimum frequency of 27Hz, and play it in Photosounder default (27.5Hz) it sounds high pitched. So there is a difference with logarithmic.
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Re: Fraction miminum frequency

Permanent link to this post Posted by steve » Tue Jun 27, 2017 9:55 am

Photosounder is not our product and we do not offer support for it, but just as an idea, perhaps you could set the spectrogram settings in Audacity to an integer value, and tweak the screenshot in a graphics editing application (such as Gimp) before feeding it into Photosounder.
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Re: Fraction miminum frequency

Permanent link to this post Posted by Piotr Grochowski » Tue Jun 27, 2017 9:58 am

How I'm supposed to know where is 27.5? And I could as well adjust the minimum frequency in Photosounder to 27.0, but then vertical flip sounds low pitched.
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