[linux-audio-dev] [linux-audio-announce] [ANN] JAPA Jack/Alsa Perceptual Analyser

Alfons Adriaensen fons.adriaensen at alcatel.be
Tue Aug 9 07:03:08 UTC 2005

On Mon, Aug 08, 2005 at 04:39:32PM -0500, Andres Cabrera wrote:

> Just tried it, and it looks very cool. Could you explain how a room can
> be tuned using japa, or point to some reference for this?

You can use JAPA as the analyser when equalising a sound system.
This is not exactly 'tuning a room', it's more making sure
that the combination of speakers and room have approximately a
flat response. Real room tuning requires more advanced and
complicated techniques, and for these you could have a look
at the combination of DRC and BruteFIR.

To do the equalisation, you need a pink noise source (future
version will have this built in), an equaliser (1/3 octave
bands or parametric), and a measurement microphone.

The setup is like this:

 pink noise  -->  equaliser --> speaker system

 microphone --> preamp --> japa

For this application (and for all noise measurements) you need 
the 'slow' speed setting. The frequency response should be set
to 'Prop'ortional, to give a flat trace with pink noise.

First make sure levels etc. are OK, then try to obtain a
flat response by adjusting the equaliser. In most cases the
best results are obtained by setting a response that is not
really flat, but drops of gently above 1 kHz, to something
between -5 and -10 dB at 10 kHz.
Trying to compensate for a deep 'holes' in the response (*)
is usually a bad idea - better try to remove the most prominent

(*) a broad response dip near the speaker crossover frequency
usually means that the relative phase of the LF and HF
speakers is wrong. 

Most synthesis programs (AMS, SC3, PD, Csound, ...) will
provide pink noise.


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