Our first meeting with John 29/9/14

I will tidy up the blog format soon.

The Meeting

Fresh back from an eye-opening weekend of climbing at Malham Cove, this morning I jumped strait into a meeting with Anro and  John  from d&b audiotechnik.

After the discussion with John, it seems his perception of the projects are far more integrated than I first thought which is a beautiful thing. Although initializing the skype call was difficult at first, it eventually worked and we got strait to business. The meeting was split into two focused sections with a slight push towards the overlapping elements of the two projects.

The notes i took down (which need to be further expanded upon) with some modification

Anros Parts:

• Dynamics in the perception of loudness
• listener fatigue from low crest factor music (over compression?)
• 12dB peak to rms on modern recordings 
• 4-5dB crest factor/dynamic range on radio
• loudness wars causing listener fatigue 
• tv advertising using the same method to make their adverts much louder
• cut high/low in dance music breakdowns, the drop causing a perceived increase in loudness - this happens in many other genres too - think Pixies - where is my mind?
• ppm6 (bbs design) - brick wall limiters on transmitter for digital output - ppm6 is peak - 8dB above 0dBu - slower decay to allow read of true peaks 
• find the really good book on level metering!!!!
• V U Meters - attempt to show perceived level - analogue components go into saturation
• Florian Camerer - a understanding of loudness - broadcast research
• Broadcasters set off a war on over-compression and increasing signal
• Find the British standard for level monitoring systems - see the attached effects on short & long term
• Florians algorithms for measurement of perceived loudness
• Application from broadcast research - application in the live sound arena at a substantial increase in level
• RESOLUTION MAGAZINE - LINEUP MAGAZINE - some history - institute of broadcast sounds
• Resolution is the upmarket studio magazine - like SOS for pros - find the lineup section - loads of info on loudness monitoring is there
• Software loudness measurement - will (hopefully) make over-loud over-compressed music defunct
• Look for broadcast sound lectures
• The effects of psychoacoustics - (have a chat with Peter Lennox intermittently)
• People expect clubs and gigs to be louder than at home/in headphones
• does the perception of the test change at different levels?
• the limiter and  attack/release time of the ear - find papers WE NEED THIS!
• Twice as loud is 10dB perceptually - the research is out there. Get it!
• 3dB is roughly twice the wattage in system terms - normally 10dB is 10 times the wattage - MONEY!
• 95dB max is normally fine for a generic theater - RnR is about 105dB - the ears protection mechanism is in effect at that level for sure
•  area under curve i.e. long-term crest factor in signals
• military research into the biology of the ears protective mechanism - and the effect of crest factor on the listening protection system - Maybe contact the RAF acoustics corps and see if they can point me towards some research

Simon Parts:

• Where the idea came from - Johns time in the uk techsupport office 
• application support - eas - club installs - DJ redline 
• jbl eons distorting to hell was "loud according to club owner - environmental differences in venue size and acoustic shape of room may have also had a factor when considering increased harmonic content??? Maybe a little bit of pride on the side of the southampton bar owner?
  JBL eons aren't exactly heavy hitters compared to DB C systems... 
• 10% harmonic distortion is the point where djz and club goers through it was loud enough? Maybe? This is according to a person John spoke to... maybe the research is out there...
• adding harmonic distortion, does it work across genres? is it just DJs? in our experience..
  that said, the FFAF engineer and some others were using techniques john mentioned earlier, to do with analogue saturation running the preamps hot and the fader low for increased details
• Are the effects of added harmonics purely psychoacoustics? 
• Crest factor (again)
  
• add harmonic distortion for improved bass?
• get example levels of harmonic distortion - see what people think - a quick and dirty listening test
• see if there is a basis for study on this topic
• Check types of distortion and patterns of harmonics... maybe the measurement of change of patterns will mean a randomized pattern choice with a smear time will be the most suitable option 
• check out inter-mod distortion too
• sort out sample and send to john

book the next meeting (done)

So my ongoing action plan for the next month

• Post up useful related literature 
• Finish proposal
• Find accurate way of measuring THD% in a system
• Plum music through that system (mat lab aplet?)
• Get samples to listen to at different 
• Go and get 30 samples of data - question based? Web Based? Headphones.
• Experiment with different types of distortion
• Experiment with level differences
• Explore crest factor more deeply

It begins today

One useful paper may be "On the Definition of Total Harmonic Distortion and Its Effect on Measurement Interpretation" by Doron Shmilovitz - although this is not audio-specific

Here is a video by Bob Katz on the loudness war:

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.