This is the webpage for a software meterbridge for the UNIX based JACK audio system.
It supports a number of different types of meter, rendered using the SDL library and user-editable pixmaps.
jack The jack library and headers must be installed.
SDL SDL version 1.2 (may work with 1.0).
SDL_image with PNG support.
The latest version is 0.9.2. Available from here as a tarball only (572kB), Planet CCRMA distribute RedHat RPMs.
su -c "make install"
meterbridge -t vu alsa_pcm:capture_1 alsa_pcm:capture_2
if you want to see what your JACK system is outputting you can use:
meterbridge -t ppm alsa_pcm:playback_1 alsa_pcm:playback_2
if you want to start a bridge with unconnected 4 meters:
meterbridge -t ppm x x x x
(or any other invalid port names)
PPM - Peak Program level Meters
Approximatly conforming to BS 6840-10. These meters are designed to indicate peak amplitude, as opposed to VU meters which are designed to indicate volume.
The scale is correct according to the standard, 4 equates to 0dB, 1 to -12, 7 to +12, and it is linear with decibels.
I've never used a real PPM meter, so I don't know if it reacts correctly. Feedback welcome.
VU - Volume Unit meters
Conforming to BS 6840-17:1991. Real meter is larger.
These meters are designed to measure the "volume" of an audio signal, it is not as relevant to digital systems as PPM meters, but is useful if you are interfacing to analogue tape, FM broadcast equipment or want a general idea of the signal volume.
The -r flag (set reference level) is useful with these meters as it will allow you to calibrate to your DA converters. The meter is pre-adjusted so that it should align correctly calibrated DA converters with analogue systems. If you wish to run with 0dBFS = 0dBu then use "-r 20"
DPM - Digital Peak Meter
Conforming to IEC 268-18:1995 (peak indicator decay may not be correct).
These are meters as typically seen on digital consoles, HD recorders etc.
There are the most efficient in screen realestate and CPU use but look a bit boring ;)
JF - "Jellyfish" Meter (aka. Goniometer)
A jellyfish meter is a stereo scope display, it can be used to spot phase and mono compatibility problems.
Some charateristic problems can be seen, eg. a signal with a stronger left channel is seen as a shape sloping to the left [\], more right slopes to the right [/], and dead mono is a vertical line [|].
The meter below the scope display indicates the degree of stereo correlation between the channels, a value of +1 means that it is perfectly mono compatible, and -1 that the channels are in anti-phase (so they will cancel out if mixed).
If someone has better examples, please mail them to me, there are probably tutorials online.
SCO - Scope
A rendering of an oscilloscope display.
It has a basic trigger function, but there is no timebase control. It renders one pixel per sample, so it will probably be next to useless at 96KHz