Making the listening test

After giving it some thought, I am going to normalize all the clean signals to -10LUFS and run the listening test at 80dbA as suggested in ITU-R BS 1770 -3

I will then have listeners change the level of a distorted file, to be the same.

This is a similar format to what the ITU did when testing LUFS for multichannel comparability.

It will also mean data can be compared fairly.

If we and LUFS are correct, the listeners should choose a level where the LUFS of the distorted signal is negligible to that of the audio signal.

A less distorted signal will be boosted more and a more distorted signal will be boosted less.

There is good evidence that LUFS is good stuff, when looking at :

The Effect of Dynamic Range Compression on Loudness and Quality Perception in Relation to Crest Factor

This not only suggests that LUFS is pretty accurate, but that a change in crest factor using dynamic range compression will effect loudness perception

Therefore, we can compare level coefficients to correlation, THD, crest factor, harmonic content, dynamic range and LUFS.


Even if the listener boosts the level of the distorted signal beyond the level of the clean signal, this will show that there is an effect on perceived loudness. 

I am going to wittle down the levels of the clipper to reduce the THD caused to a 1kHz sine wave to roughly 0 - 20% THD. This is because beyond this level, the distortion is very audible and I want to minimize the subjective effects of distortion on results. 20% THD is audible enough as it is. A further study could look at those levels of THD. Other studies previously referenced have proven that distortion becomes audible beyond 15% THD, when compared with the effects of clipping on a pure tone.

This will also allow me to slip the signals through other nonlinearities which function with frequency, and see how the different harmonic patterns compare.

I need to learn how to make waterfall plots for these signals. Maybe spectrographs will have to do?

Anyway.

Nonlinear dynamics

https://www.youtube.com/watch?v=Y0u3o9_BRVQ

Anyway, it has been a little while (i think) since I updated this blog.

Stuff is moving along well. The listening test is due for a slight modification.

Next up I am going to apply the LUFS measurement algorithm in matlab, and use it to process the loudness of all audio files used, to ensure a solid LUFS level.

I will then standardise the listening conditions to a particular LUFS measure using a dumy head and the listening test rig, to ensure everything is the same. I can then increase the LUFS on the test rig to test different loudness effects on the effects of DISTORTION on perceived loudness.

I cannot directly link only THD to perceived loudness in musical signals, so I am just going mainly for a distortion characteristic now,

Also, I will evaluate crest factor and other bits with the data I accrue to get a more accurate picture of the systems involved.

Finally I will perform some cross-correlation analysis on audio that has been passed through nonlinear devices, to give a number to amounts of distortion, even if it isn't a traditional distortion metric. I am also modifying the listening test to get relative loudness measures between a clean and distortion version of a signal, so we can find what the level change is for perceptual level difference.

Good stuff.

It is just a shame that I have no listening test data yet.
I am also thinking about simplifying the listening test, to make it less prone to error.