[Consortium] audio meters nostalgia

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.