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PostPosted: Mon Sep 03, 2018 1:51 am 

Joined: Sat Feb 21, 2015 10:53 pm
Posts: 29
This would be a niche-use application, but it would be cool to be able to upsample and re-dither 16-bit 44,100 lossless audio to 24-bit 88.2 / 96Khz with the missing harmonics/overtones/resonant frequencies added back in, regardless of processing power the calculations would take. The result could 'sound' better/smoother due to lack of modular distortion that can occur when simply recording at a high sample-rate.

Of course, I realize this is a touchy subject for some people, but hey, if we can do the math I say, why not? There used to be a piece of software that would do this called 'Any Time' but it seems to be long-gone. Used to take about an hour to calculate one audio track. Of course with my 20-core workstation, shouldn't take nearly as long :D I don't know of anyone else out there who has done it since.

The results on a frequency analyser, at least visually, were pretty impressive.

I included a result below, this took 15 hours :o to complete as the program is only single-threaded

From the Help-file:

"Under [ High frequency range extrapolation ] you can enable a unique feature that adds over-tones to the upper frequency range (this is only applicable when decreasing the pitch and/or increasing the sample rate where an otherwise "empty" upper frequency region would otherwise be present). It does this by analyzing the input audio and determine the both highest component-tones, and the "frequency envelope" at every instance, then extrapolating the frequency envelope upwards and synthesizing a series of over-tones. The amount of audio energy in the synthesized overtones can be controlled by a Spectral slope parameter (this is expressed as a "dampening per octave factor"). You can also control if all harmonic over-tones or only a select few (only even over-tones, or only a geometric series of over-tones) shall be synthesized. Note that the program will only produce harmonic overtones - i.e. ones that sound good to the ear! There very few other programs that can extrapolate higher frequencies (e.g. one is used in the "mp3Pro" or "AAC+" formats, where they call it "synthetic bandwidth extension"), and in our experience far from all of those few existing seem to even obey that simple principle of producing harmonic over-tones..."


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PostPosted: Mon Sep 03, 2018 9:20 am 
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Joined: Tue Sep 15, 2015 12:22 pm
Posts: 362
The 16-24 bit thing is already there, it's called dequantizer and is part of the Repair section of Stereo Tool.
Absolute highs could help you to generate missing highs, though it doesn't go that high.

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Imaging producer & Stereo Tool audio processing consultant


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PostPosted: Sat Sep 08, 2018 1:45 am 

Joined: Sat Feb 21, 2015 10:53 pm
Posts: 29
Quote:
The 16-24 bit thing is already there, it's called dequantizer and is part of the Repair section of Stereo Tool.
Absolute highs could help you to generate missing highs, though it doesn't go that high.
I am familiar with the Dequantizer and the Absolute Highs... Any way to override the default cutoff filter to calculate up to 40khz? I'd only want to recreate frequencies from the cutoff filter set on CDs, usually around 19.5-20Khz.

I did export all settings and check them with Notepad++, didn't see any setting for the internal cutoff filters...


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PostPosted: Wed May 26, 2021 10:12 pm 
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Joined: Sat Aug 31, 2019 9:44 pm
Posts: 28
Location: VA USA
I'm curious. Did Absolute Highs ever get the option to remove the limit?
There are some tests that I would like to do, if it did, but they're not really needed.

I also know that it can't work miracles. I have some recordings sampled at 22050 Hz. Absolute Highs does a great job of restoring frequencies missing from 11025 Hz to 22050 Hz, but I can never get it to restore above that even with multiple passes. On a normal 44100 Hz sampled recording, it will add frequencies up to 24000 Hz, if upsampled to 48000 Hz. I'm guessing the amount of data missing limits how much can be calculated. Maybe upscaling from 44100 Hz to 96000 Hz would yield similar results as 22050 Hz to 48000 Hz.


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