[LAU] audio meters nostalgia

[Mark Knecht]

Great stuff. thanks!

- Mark

On Sat, Apr 12, 2008 at 7:56 AM, Fons Adriaensen <fons at kokkinizita.net> wrote:
> The first (beta) release of Jmeters is available at
>  <http://www.kokkinizita.net/linuxaudio/downloads>
>
>  Jmeters is a Jack multichannel audio level meter app.
>  It looks very similar to meterbridge since it uses the
>  same pixmaps.
>
>  This first release offers VU, PPM and stereo versions of the
>  same. The stereo versions have two indicator needles on the
>  same scale. I've never seen a twin VU, but stereo (or M/S)
>  PPMs *do* exist. Later releases will add bargraph meters,
>  digital peak indicators for the analog ones, and a stereo
>  correlation meter.
>
>  The main difference to meterbridge is that Jmeters has the
>  correct ballistics for both the VU and the PPM.
>
>  The VU meter measures the average of the absolute value of
>  the signal, 'average' meaning a second order filter that
>  reaches 99% in 300ms and overshoots between 1.0 and 1.5%.
>  It is calibrated to indicate 0dB for a sine wave at -10dB
>  w.r.t. digital full scale (which is +/-1 peak in this case).
>
>  The particular VU scale used is not entirely linear and
>  starts at -20dB (it's one designed for a passive VU meter
>  with a diode bridge), so the meter will not move at all
>  for inputs below that level. Later versions may use a
>  VU scale designed for an active meter which doesn't have
>  this threshold.
>
>  The PPM is a pseudo-peak meter. It will indicate 80% of
>  the steady-state value for a 10ms burst, and fall by 24db
>  in 2.8s. Each scale division (1..7) represents 4dB. It is
>  calibrated to indicate '7' (+12 dB on the EBU scale) for
>  0dB FS.
>
>  For speech and music with distinct short peaks the PPM
>  will usually indicate higher. For music with continuous
>  long notes, and for heavily compressed signals the VU
>  indicates higher. Both meters require some 'getting used
>  to' in order to read them correctly.
>
>  You can modify the calibration by using the -g(ain) option,
>  but it should normally not be necessary.
>
>
>  Enjoy !
>
>
>  --
>  FA
>
>  Laboratorio di Acustica ed Elettroacustica
>  Parma, Italia
>
>  Lascia la spina, cogli la rosa.
>
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