MY IEP FIRST POST

25/9/14

The Project

Over the summer months I have been researching towards my Independent Engineering Project, which is the 'dissertation' for my degree 'BSc (Hons) Sound, light & Live Event Technology at the University of Derby. 

Along with this module, I have taken on 'Embedded Systems', 'Audio Digital Signal Processing', 'Live Event Practice' and 'Electro-acoustics & Lighting Design'. This should prove to be a monster year!

I was contacted a few weeks ago by a lecturer, who has devised a number of possible IEP projects which will involve being mentored by John Taylor from D&B Audiotechnik. This large and small format loudspeaker and peripheral manufacturer is not only famous for incredible bottom end, but its use of DSP which is something I am very interested in.

After bidding for the project, I was offered the chance to take it on along with another student. After some discussion and the toss of a coin, we chose the elements of the project we wish to work on.

The Background

So the story goes that Mr Taylor goes on occasion to a club where D&BA have installed a sound system. When he visits, the system is often in a state of saturation and high THD as it is pushed too hard, When he fixes the system, the club and clients complain that it is too quiet. As we know, an amplifier can only push out so much level, and no more. When pushed harder, the amplifier will distort the signal and may not get physically louder. As such the question arises, does increased THD make sound subjectively louder?

My initial approach to this is that in principal, yes. Consider energy output as a graphical curve:

• An amplifier may only attenuate so much power (W) 
• If you push an amplifier to produce more power that it can handle it saturates, thus introducing more harmonics (distortion). Thus the waveform is changed. 
• In the instance that this distortion is constructive (considering interference), more harmonics means more energy dissipated under the curve across the frequency domain. 
• An increase in spectral content, even at the same level may excite more of the basilar membrane and may thus be perceived as louder due to a increased energy transfer. 

Thus my IEP will be test research, implement and test methods of adding THD into signals at a constant peak and average level, to discern objective and perceptive loudness (increase or decrease) with different levels and styles of THD added. 

The Major Questions

• Are we so used to distortion that we expect it? Do we need it?
• Is there a link between THD and the increase in feeling the music (getting punched with bass)
• Could the introduction of THD be beneficial to audio-reproduction both in the isolated and free listening formats (headphones and in the club/field)
• Could adding the correct kind of distortion save loudspeaker systems?
• Does increased THD actually increase the energy output by a loudspeaker/system?

I am now beginning my project proposal.