16-02-2013, 10:20 AM
Beyond MP3, Soundfield analysis, perception, and capture or synthesis.
Beyond MP3.ppt (Size: 1.97 MB / Downloads: 18)
The Origins of Audio
Audio, in the way we use it here, is the technology, science,
and art of recording or creating something to be played back
via transducers to the human auditory system. The musical
issues are not included, and indeed warrant a separate and
serious discussion by an expert in the subject.
There have been several varieties of recording and/or transmission
methods, starting with none, i.e.:
Live Performance
Acoustic Recording of Live Performance
Electronic Recording of Complete Performance
Studio Recording of Individual Sessions
Direct Synthesis of Music
WHAT DID I JUST SAY?
Well, it’s not all bad news. There are things that both older
and newer recording methods do very well. What are they?
1) Capture, at one or more points, the pressure, velocity, or 3d pressure/velocity of the sound at a given point in the atmosphere.
2) Store that in a secure, accurate, and easily reproduced and/or
transmitted form.
3) Reproduce/amplify that recorded (set of) pressures, velocities, and such as electrical analogs.
What do we do an “ok” job with?
In a word, loudspeakers. While it’s no doubt that loudspeakers
are far and away the weakest link in the array of equipment, they
are still not too bad. They can reproduce most of the dynamic
range, over most of the frequency range, and (if you spend your
money wisely) at a level of distortion (in the waveform sense) that is at least sufferable, if not perfect.
What loudspeakers can’t do, however, is replace what was lost
at the original acquisition, or replace what was never extant in the
recording to begin with. Unfortunately, loudspeakers are
very often called upon to do exactly that.
What are we missing?
In a real venue, the soundfield is very complex, and we
sample it as we move and turn our heads. The soundfield in any reverberant performing venue will change in less than one wavelength at any given frequency.
That is to say, at 1 kHz, 1 foot, give or take, will yield a
substantially different soundfield. In venues with highly
dispersive reverberation (which is an ideal), in fact, the
coherence length of a signal may be substantially less than a wavelength under some important and realistic conditions.