[LAD] Determining Phase

Jörn Nettingsmeier nettings at folkwang-hochschule.de
Sun Jun 26 09:58:54 UTC 2011

On 06/26/2011 10:50 AM, pshirkey at boosthardware.com wrote:
>> So, perhaps any Haas-effect plugin would satisfy Patrick's needs.

so this is about panning? that's actually pretty easily done with just a 
time delay in addition to level difference. unless you want to spread 
complex sounds out in space, in which case you replace the delay with a 
frequency-dependent allpass.

careful with the term "haas effect". all the poor guy did was check the 
time window in which an echo would not be perceived as a separate event. 
basically, the haas effect says you can get hide a P.A. delay system 
that's 10dB louder than the main P.A. if it hits between 10 and 30ms 
later, and still maintain good "on-stage" localisation, with the delay 
being practically inaudible.
sometimes also called the "law of the first wavefront".

this has nothing to do with stereo localisation. time delays relevant 
for left-right localisation are in the 0 - 1ms range, some authors give 
a bit less, others a bit more.

>> Other than that, I'd make a really cool spectrum analyzer that ran the
>> Fourier analysis on two channels, correlated their phases then made a
>> +/- line vs. frequency for all to see so that the phase of the
>> components of the spectrum could be watched for phase relationships.

that is precisely what dual-fft tools for p.a. system calibration do, 
and they're extremely useful.
they allow you to constantly monitor the system with _program_ material, 
without having to use MLS noise or any other specific measurement signal.
one channel is used for the direct signal from the mixer, the other is 
fed by a measurement microphone with delay compensation. you get instant 
phase and amplitude response. good systems also give you an additional 
"confidence" curve that tells you how much you can trust which parts of 
the spectrum. for instance, if your program material is a boy soprano, 
the confidence of the measurement in the low end is practically zero.

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