Disable automatic low pass filter when resampling

[8bit_coder]

First off I'm using windows 8.1 Pro and Audacity 2.2.2

Whenever I resample something in audacity, it resamples it but it also has an automatic low pass to prevent the alias frequencies from coming through. Is there a way I can disable this to hear for example a 8 khz sample rate file without the low pass, meaning including all of the hiss and alias noises along with that sample rate?
Thanks.
PS: I am willing to modify code in my copy of audacity to attempt this

[DVDdoug]

PS: I am willing to modify code in my copy of audacity to attempt this

You'll probably have to do that. Filtering is part of any proper downsampling algorithm. I've never even looked at the Audacity code but I assume you know it's open source.

You can probably make a Nyquist plug-in. That should be easier than modifying the Audacity code and I'd imagine it's "easy" if divide the sample rate by even numbers.

[8bit_coder]

Well, then what code should I write? I don't have a ton of experience with nyquist so a little help would be greatly appreciated

[Trebor]

First off I'm using windows 8.1 Pro and Audacity 2.2.2

Whenever I resample something in audacity, it resamples it but it also has an automatic low pass to prevent the alias frequencies from coming through. Is there a way I can disable this to hear for example a 8 khz sample rate file without the low pass, meaning including all of the hiss and alias noises along with that sample rate?

A similar effect could be achieved with a bit-crush plugin.
Tritik Krush is free & works in Audacity on Windows ...

https://youtu.be/owZhhsHjh20?t=35s

[steve]

Whenever I resample something in audacity, it resamples it but it also has an automatic low pass to prevent the alias frequencies from coming through. Is there a way I can disable this to hear for example a 8 khz sample rate file without the low pass, meaning including all of the hiss and alias noises along with that sample rate?
Thanks.

1) Select the track
2) Apply this command in the Nyquist Prompt:

Code: Select all

;version 4
(force-srate 8000 *track*)

3) From the track drop-down menu, select "Rate" and set it to 8000.

The "force-srate" command resamples a sound using linear interpolation without pre-filtering.
*TRACK* is a special variable that passes the selected audio from Audacity to Nyquist.

By the way, the current and recommended version of Audacity is 2.3.2. It is available via the Audacity website: https://www.audacityteam.org/download/windows/

[8bit_coder]

To Steve's solution:

Yes, I know of that nyquist command. But it still acts the same as if I just clicked resample. This simply does that but in a more complicated way and it doesn't give the results I want.

To the Trikit solution:

Yes, I know I can use a bit crusher, but that defeats the whole purpose of being able to set a specific sample rate.

Thanks

[kozikowski]

that defeats the whole purpose of being able to set a specific sample rate.

Reducing the sample rate isn't "free." 8000 is just better than AM radio.

What's the goal? I mean the real goal, not the microscopic viewing the rate goal. Why are we doing this?

Koz

[Trebor]

To the Trikit solution:
Yes, I know I can use a bit crusher, but that defeats the whole purpose of being able to set a specific sample rate.

Tritik Krush does also downsampling as well as bitcrush.
dBlue crusher is a free plugin which has a downsample slider, independent of bitcrush.

[steve]

To Steve's solution:

Yes, I know of that nyquist command. But it still acts the same as if I just clicked resample.

Try following the instructions exactly as I wrote them.

[Trebor]

Try following the instructions exactly as I wrote them.

Code: Select all

;version 4
(force-srate 8000 *track*)

In Audacity 2-3-2 on Windows 8 that code just speeds it up.