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(***edit positions filled***)

I have just purged inactive moderators, so there is a few new openings.

Put your name forward here, if we can get another 3 global moderators, to mainly deal with spam, and enforce HA TOS with precision, no audio-foolerly here.

Preference will be given to those who have interacted the most with the forum, for the longest.

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🎵 VLAK – Lossless Audio Codec
🕰️ History & Motivation
This project is a digital relic from the early days of modern computing, originally developed by a group of students during their Computer Science studies at the Warsaw University of Technology in the 2005/2006 academic year (05Z semester).
Motivation for revisiting this project is two-fold:

• 🗃️ Preservation – To safeguard the source code and intellectual property we created, ensuring it remains accessible to future generations.
• 🤖 Modernization – To experiment with AI-powered tools in order to restore and refactor this legacy codebase.

📌 Goal
The project aimed to create a lossless audio codec (bit-perfect compression without quality loss) as an alternative to popular lossy codecs such as MP3 and OGG.
Main applications include:

• archiving CD-quality music,
• professional audio processing,
• audiophile use,
• bootlegs and live recordings,
• portable music players.

Continue Reading: https://github.com/malipio/vlak#readme
📚 Documentation: Original - PDF - report (in polish 🇵🇱)
📝 License: This project is licensed under the MIT License

Source: https://github.com/malipio/vlak

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UPDATE 27nd November  (nearly complete). Find it here:

https://src.hydrogenaudio.org/

To test a SRC:

https://src.hydrogenaudio.org/upload


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It is proposed to implement an automated method of testing and showing the results for various digital transformations / filters / resampling here on HydrogenAudio. Starting with Sample Rate Conversion (note aware of the good work done by https://src.infinitewave.ca/  ), we propose a test suite where samples can be downloaded, uploaded and results processed automatically here, with a custom section dedicated to each function.

Having looked about the place, this is a good basis for testing:

https://www2.spsc.tugraz.at/www-archive/downloads/Mueller11_DopplerSRC_0.pdf

Looking for feedback on these tests, RMAA also does various tests, and can be looked at also.

Initial thoughts are to test up and down resampling separately, at frequencies most likely to be used in the real world.

The paper above tests:

Impulse Response
A signal with a sample rate of 96 kHz is downsampled to 44.1 kHz. The signal x[n]
consists of 96000 gcd(96000,44100) = 320 unit impulses with enough space between them. The im-
pulses are at sample positions n so that {n mod 320} is a permutation of {0, 1, 2, . . . , 319}.
This basically means that all fractional differences in sample positions between input
and output signal are addressed exactly once. In the later analysis the output signal is
upsampled (by inserting zeros) to lcm(96000, 44100) = 14.112 MHz and the impulse re-
sponses are added to obtain a high resolution impulse response, which is also inspected
in the frequency domain in phase and magnitude utilizing the DFT.

Dynamic Ratio
A sine wave at a frequency of 5 kHz with a sampling rate of 48 kHz is resampled to a
linear chirp between 100 Hz and 20 kHz over 10 seconds simulating the Doppler effect
of a passing object. For analysis the spectogram of the resulting file is plotted.

Sweep
A sweep signal with a linear slope of 1 kHz/s from 1 Hz to 48 kHz at a sample rate of
96 kHz is downsampled to 44.1 kHz. Again the spectogram is plotted for analysis to
evaluate aliasing effects and filter cutoff.

Aliasing
A 23 kHz sine at −4 dBFS with a white noise floor of −150 dBFS over 30 seconds is
downsampled from 96 kHz to 44.1 kHz. The resulting signal is analysed using Welch’s
method with 4 segments, an overlap of 50 %, and a Hann window.

Harmonic Distortion
Equivalent to the Aliasing test, with the only difference that the sine has a frequency
of 1 kHz.

Intermodulation Distortion
Again equals the Aliasing test with the difference that the sine is replaced by two sines,
one at 60 Hz, −6 dBFS and the second at 7 kHz, −18.0412 dBFS, which equals quarter
the amplitude of the first sine