3.7 KiB
FM95 config file
By default the config file path is on /etc/fm95.conf, it's a ini formatted config consisting of this syntax:
[section]
key=value
Audio Pipeline
Pulse -> Audio Preamp -> AGC -> LPF -> Pre-Emphasis -> Audio Volume -> Audio Clipper -> Stereo Encoder -> BS412 -> Master Volume -> Output Clipper
Below are the sections and their keys
fm95
stereo
Simple boolean, set to 0, or 1
rds_streams
Integer from 0 to 4, it sets how many channels to capture from RDS95, note that both values have to match, otherwise god may have mercy on your RDS decoders
clipper_threshold
Sets the peak to peak value of the Audio Clipper, defaults to one, but can be disabled by setting 0
preemphasis
Sets the Preemphasis tau, basically how much highs is boosted, by default and in Europe it is 50µs, but in the USA and South Korea, use 75µs. Expects unit in integer microseconds
calibration
Simple integer, set to 1 to output a sine wave at 400 Hz, which should correspond to 75 KHz deviation by default. Set to 2 for a 60 Hz square wave, this test is to set the tilt, more on which later
master_volume
Float value to set the master volume, 1 by default, set to 0 to mute MPX
audio_volume
Float value to set the audio volume, also 1 by default, set to 0 to mute audio itself, but stereo pilot and RDS should remain
audio_preamp
Pre-amplification of the audio, before any filters, set to 1 by default, set to 0 to mute audio
deviation
Set the deviation, you can use this to easily change to 50 KHz deviation if needed, by default 75 KHz, under the hood it just sets the master volume to x/75000. Expects unit in Hz
tilt
This is needed for most DACs, as they have output high pass filtering for DC, such filtering is not phase-linear, for example when DC is played, it will slowly go back to 0, such filtering is bad for square waves and some bass, use calibration 2 to test for tilt, you can use a oscilloscope with a receiver or a RF spectrometer as well as a SDR, if in tilt, you should see a perfect square wave, a signal abruptly jumping between 1 and -1 on a oscilloscope or a signal jumping between -75 and 75 khz on a RF spectrum, for the setting itself this is a simple float with values between 0 (off) and 1
bs412_max
This is usually not needed to set, but it sets the max gain for the BS412 compressor, so if it is the default 1, the BS412 compressor will never make the signal louder than it is on the input
agc_target
Target of the AGC, usually not needed to set, defaults to 0.625 (higher is louder)
agc_attack
How fast will the AGC react to the signal going over the target, unit in seconds
agc_release
How fast will the AGC react to the signal going lesser than the target, in seconds
agc_min
Default is 0.1, this is usually not needed, for what it does, see bs412_max, but instead of louder quieter, and not bs412 but agc
agc_max
See agc_min, but its louder not quieter, and the default is 1.5
bs412_attack
See agc_attack, but BS412, not AGC
bs412_release
See bs412_attack, but its release instead
advanced
lpf_order
Sets the quality of the LPF, unless running on a weak system, this does not need change from the default 15 (lower is less cpu usage)
preemp_unity
Sets the unity gain for preemphasis, if you don't know what that means you shouldn't touch this, but it defaults to 15 khz, unit in hz
sample_rate
Default 192 khz, does not need change under most systems, and unit is in hz
lpf_cutoff
lpf cutoff, some run this at 15, because Big FM™ tells them to, but running this higher has no costs (unless you're running it above 18.5 khz), but no gains either, unit in hz