Jmeters-0.4.1   6/11/2012
-------------------------

Jmeters is a Jack app offering software versions of various
analog audio level meters.

This release offers VU meters, BBC, EBU and DIN style PPM
meters, stereo versions of the three PPMs, and correlation
meters matching the VU, BBC and DIN styles, most of them in
different sizes and shapes.

The important difference to Meterbridge is that the Jmeters
instruments have the correct 'ballistics' for both the VU and
the PPMs. Given the same input, they will react exactly as the
original electro-mechanical meters, all of which are rather
strictly specified in various standards documents.

The default 'style' is now a rectangular 'moving coil' meter
of around 300 by 170 pixels. This can be modified by using the
-f(rame) option. There is also a smaller rectangular style, and
the two original round styles (inherited from Meterbridge) are
still available. Most but not all combinations of meter and frame
type are possible. The exceptions are the DIN style PPM which
exists only in the rectangular styles, and the stereo correlation
meters which are not offered in the larger rectangular size (it
really makes no sense to make them that big). Starting from this
release, the meter 'needles' are plotted using the Cairo library,
which provides much better visual quality than raw X11 graphics.

It is now possible to put labels on the meters, just include
them on the command line, either mixed with the Jack port names
or after them. A string containing a ':' is interpreted as a
Jack port, or as a label otherwise. If you use only labels the
inputs will remain unconnected. Labels for the old round styles
should be short.

Some info on the meter types:

The VU meter measures the average of the absolute value of the
signal, 'average' meaning a second order lowpass filter (which
was originally the mass + spring + damping system of the meter
movement) that reaches 99% in 300 ms and overshoots between 1.0
and 1.5%. It is calibrated to indicate 0 dB for a sine wave at
-20 dB FS. 

The PPM is a quasi-peak meter which means it does not indicate
the real digital peak value, but it will react to short bursts
much faster than a VU and fall back slower. The BBC and the EBU
variations are identical except for the scale marks. They will
indicate -2 dB relative to the steady-state value for a 10 ms
burst of a 5 kHz sine wave, and fall back by 8.7 dB per second.
They are calibrated to indicate '4' on the BBC scale or 0 dB
(shown as 'TEST') on the EBU scale for a -18 dB FS sine wave.
Earlier versions had the 10 ms integration time right but did
indicate a few dB lower than required by the IEC 'type II' specs
for shorter bursts. This has been fixed in this release. Many
thanks to Richard Lamont for pointing out these errors (and for
writing the excellent Wikipedia article on PPMs). 

The DIN style PPM is an IEC 'type I' meter. Apart from having a
wider dynamic range scale, it has a faster rise time (5 ms instead
of 10 ms) than the BBC or EBU versions and also falls back a bit
faster (when measured in dB/s - given the larger range it appears
to fall back slower). Reference level (0 dB indicated) is -9 dB FS.

All these level meters require some 'getting used to' in order to
read them correctly. The calibration can be modified by using the
-r(eflev) option, but this should normally not be necessary.

The stereo correlation meters are all identical except for the
scales. For a sine wave input the value indicated is the cosine
of the phase difference between the two inputs.

Enjoy !

-- 
FA