And now... Eternity.

Not a comment on infinite regression, though that seem to describe the pattern of the quality of my humour. I am getting pretty frustrated with measuring the THD of music, as opposed to sine waves.

This week so far has been busy, much like any other week but more so. 

I came strait out of a trip to north Wales, into a frenzy of work on my proposal followed by two days of reproduced sound. Yesterday I handed in the proposal. 

I will make it available to you all, and discuss some of the points I found while writing it, in this blog.

Although I said what I needed to say in it (or at least I think so), I feel the proposal was possibly too concise. The volume of references was roughly a similar size to the problem definition and aims.

I had actually finished the proposal about a week before submission, but as always not to a standard I thought was good enough. I thought it would pass, but it wasn't really the standard I thought represented what I wanted to do. My only fear is that the current version is too concise as I have said. We shall see. 

So I refined my search terms/methods and found a vast array of research, into the perception of audio quality and its relationship with distortion. There are already many models around for measuring and predicting distortion, this study may be able to go to a depth I didn't consider before hand.

A particularly good paper is 'Detection of nonlinear distortion in audio signals' by S Mare, which has provided a great look into a method of detecting distortion without needing the original signal for comparison. The really useful thing is the definition of terms and equations available. As it turns out, the IEEE seem to have plenty of research papers which look particularly deeply into THD in reference to power systems, which may undoubtedly come into use at some point. I am starting to think that THD really isn't the be all and end all of distortion measures though.

My THD calculation software is now fully working for the pure sine waves, the problem was in the array addressing.

I am currently looking for papers which focus on nonlinear polynomial distortions, to try and model some realistic system behaviour. It is all go.

It is also interesting to see how many papers which describe THD and methods for measuring related audio quality, nod towards perceived loudness without going into real detail. Voishvillo's 2006 paper 'Assessment of Nonlinearity in Transducers and Sound Systems – from THD to Perceptual Models' is a particularly good example of this. 

I do find it particularly interesting that the recent post-grads who presented at reproduced sound this year, seemed to focus particularly on a mathematical model and not on the aim of using the model.

Foot note:

One of the studies presented at reproduced sound was looking at the quality of internet audio, and how people rate it. As we sat in the lecture, various samples were played. Given the videos were not normalised, I felt that the more distorted audio signals presented sounded louder but not in a good pleasing way, in the instances that they were at the same level i.e. increased level w/m^2 and loudness is not the same thing when taking spectral distribution into account.

Maybe my listening test could be an online one. I would get a more diluted data set, but the increase in participant numbers may help statistically.