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change the config file stuff

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KubaPro010
2025-08-03 17:20:33 +02:00
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208
fm95.md
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@@ -1,126 +1,106 @@
# FM95 Configuration File
# FM95 config file
This document describes the configuration file format for the FM95 FM transmitter software.
## File Format
The configuration file uses standard INI format with sections and key-value pairs. Comments can be added using the `#` or `;` character at the beginning of a line.
## Configuration Sections
### [fm95] - Main Settings
This section contains the core FM95 transmission parameters.
#### Audio Processing
- **`stereo`** (0 or 1, default: 0)
Enable stereo transmission. Set to 1 for stereo, 0 for mono. Or set to 2 for Polar Stereo
- **`audio_volume`** (float)
Audio input volume multiplier. 1.0 = unity gain, values > 1.0 may cause distortion.
- **`master_volume`** (float)
Master output volume control. Affects overall transmission level.
- **`clipper_threshold`** (float)
Audio clipper threshold to prevent overmodulation. Lower values = more aggressive clipping.
- **`preemphasis`** (float, microseconds)
Pre-emphasis time constant in microseconds. Common values: 50 (Europe), 75 (North America).
#### RDS (Radio Data System)
- **`rds_streams`** (integer, range: 1-4)
Number of RDS data streams to process simultaneously. More streams allow richer RDS data but require more processing power.
#### MPX (Multiplex) Settings
- **`mpx_power`** (float)
MPX signal power level. For BS412.
- **`mpx_deviation`** (float, Hz)
Maximum frequency deviation for MPX signals. Standard value is 75000 Hz for FM broadcast.
#### Calibration
- **`calibration`** (0-2, default: 0)
Enable calibration mode for testing and adjustment. (2 enables 40 hz square wave instead of the 400 hz sine)
#### Frequency Deviation
- **`deviation`** (float, Hz)
Maximum frequency deviation. Standard FM broadcast uses 75000 Hz. This setting affects the master_volume automatically.
### [devices] - Audio Device Configuration
This section specifies the audio devices to use for input and output.
- **`input`** (string, max 63 chars)
Primary audio input device
- **`output`** (string, max 63 chars)
MPX input
- **`mpx`** (string, max 63 chars)
MPX (multiplex) input device for subcarrier input
- **`rds`** (string, max 63 chars)
RDS signal input
## Example Configuration
By default the config file path is on /etc/fm95.conf, it's a ini formatted config consisting of this syntax:
```ini
# FM95 Configuration File
# Lines starting with # are comments
[fm95]
# Enable stereo transmission
stereo=1
# Audio levels (1.0 = unity gain)
audio_volume=0.8
master_volume=1.0
# Prevent overmodulation
clipper_threshold=0.9
# Pre-emphasis for Europe (50µs) or North America (75µs)
preemphasis=50
# Enhanced stereo processing
polar_stereo=1
# RDS configuration
rds_streams=2
# MPX settings
mpx_power=0.1
mpx_deviation=75000
# Standard FM deviation
deviation=75000
# Enable calibration mode for testing
calibration=0
[section]
key=value
```
## Important Notes
## Audio Pipeline
1. **RDS Streams**: Maximum of 4 RDS streams are supported. Exceeding this limit will cause an error.
`Pulse` -> `Audio Preamp` -> `AGC` -> `LPF` -> `Pre-Emphasis` -> `Audio Volume` -> `Audio Clipper` -> `Stereo Encoder` -> `BS412` -> `Master Volume` -> `Output Clipper`
2. **String Length**: Device names are limited to 63 characters maximum.
Below are the sections and their keys
3. **Deviation Interaction**: The `deviation` setting automatically adjusts `master_volume` using the formula: `master_volume *= (deviation / 75000.0)`. Set deviation last if you want to override master_volume.
## fm95
4. **Audio Levels**: Keep audio levels reasonable to prevent distortion. Start with conservative values and adjust as needed.
### stereo
5. **Preemphasis**: Use 50µs for European broadcast standards, 75µs for North American standards.
Simple boolean, set to 0, or 1
## Troubleshooting
### rds_streams
- **No audio**: Check device names with system audio tools
- **Distorted audio**: Reduce audio_volume and clipper_threshold
- **Poor stereo separation**: Enable polar_stereo and adjust mpx_power
- **RDS not working**: Verify rds device and ensure rds_streams ≤ 4
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 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

50
src/fm95.c
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@@ -315,26 +315,36 @@ static int config_handler(void* user, const char* section, const char* name, con
pconfig->audio_preamp = strtof(value, NULL);
} else if (MATCH("fm95", "deviation")) {
pconfig->audio_deviation = strtof(value, NULL);
} else if(MATCH("fm95", "tilt")) {
pconfig->tilt = strtof(value, NULL);
} else if(MATCH("fm95", "bs412_max")) {
pconfig->bs412_max = strtof(value, NULL);
} else if(MATCH("fm95", "agc_target")) {
pconfig->agc_target = strtof(value, NULL);
} else if(MATCH("fm95", "agc_attack")) {
pconfig->agc_attack = strtof(value, NULL);
} else if(MATCH("fm95", "agc_release")) {
pconfig->agc_release = strtof(value, NULL);
} else if(MATCH("fm95", "agc_min")) {
pconfig->agc_min = strtof(value, NULL);
} else if(MATCH("fm95", "agc_max")) {
pconfig->agc_max = strtof(value, NULL);
} else if(MATCH("fm95", "bs412_attack")) {
pconfig->bs412_attack = strtof(value, NULL);
} else if(MATCH("fm95", "bs412_release")) {
pconfig->bs412_release = strtof(value, NULL);
} else if(MATCH("advanced", "lpf_order")) {
pconfig->lpf_order = atoi(value);
} else if(MATCH("advanced", "preemp_unity")) {
pconfig->preemp_unity_freq = strtof(value, NULL);
} else if(MATCH("advanced", "sample_rate")) {
pconfig->sample_rate = atoi(value);
} else if(MATCH("advanced", "agc_target")) {
pconfig->agc_target = strtof(value, NULL);
} else if(MATCH("advanced", "agc_attack")) {
pconfig->agc_attack = strtof(value, NULL);
} else if(MATCH("advanced", "agc_release")) {
pconfig->agc_release = strtof(value, NULL);
} else if(MATCH("advanced", "agc_min")) {
pconfig->agc_min = strtof(value, NULL);
} else if(MATCH("advanced", "agc_max")) {
pconfig->agc_max = strtof(value, NULL);
} else if(MATCH("advanced", "bs412_attack")) {
pconfig->bs412_attack = strtof(value, NULL);
} else if(MATCH("advanced", "bs412_release")) {
pconfig->bs412_release = strtof(value, NULL);
} else if(MATCH("advanced", "lpf_cutoff")) {
pconfig->lpf_cutoff = strtof(value, NULL);
if(pconfig->lpf_cutoff > (pconfig->sample_rate * 0.5)) {
pconfig->lpf_cutoff = (pconfig->sample_rate * 0.5);
fprintf(stderr, "LPF cutoff over niquist, limiting.\n");
}
} else if(MATCH("volumes", "mono")) {
pconfig->volumes.mono = strtof(value, NULL);
} else if(MATCH("volumes", "pilot")) {
@@ -345,16 +355,6 @@ static int config_handler(void* user, const char* section, const char* name, con
pconfig->volumes.rds = strtof(value, NULL);
} else if(MATCH("volumes", "rds_step")) {
pconfig->volumes.rds_step = strtof(value, NULL);
} else if(MATCH("fm95", "tilt")) {
pconfig->tilt = strtof(value, NULL);
} else if(MATCH("advanced", "bs412_max")) {
pconfig->bs412_max = strtof(value, NULL);
} else if(MATCH("advanced", "lpf_cutoff")) {
pconfig->lpf_cutoff = strtof(value, NULL);
if(pconfig->lpf_cutoff > (pconfig->sample_rate * 0.5)) {
pconfig->lpf_cutoff = (pconfig->sample_rate * 0.5);
fprintf(stderr, "LPF cutoff over niquist, limiting.\n");
}
} else {
return 0; // Unknown section/name
}
@@ -502,7 +502,7 @@ int main(int argc, char **argv) {
.bs412_attack = 0.05f,
.bs412_release = 0.025,
.bs412_max = 1.0f,
.lpf_cutoff = 15000, // 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
.lpf_cutoff = 15000,
};
FM95_DeviceNames dv_names = {