part 2?

fm95.md

@@ -0,0 +1,131 @@
+# FM95 Configuration 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.
+
+- **`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).
+
+#### Stereo Processing
+
+- **`polar_stereo`** (0 or 1, default: 0)  
+  Enable polar stereo encoding.
+
+#### 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
+
+```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
+
+```
+
+## Important Notes
+
+1. **RDS Streams**: Maximum of 4 RDS streams are supported. Exceeding this limit will cause an error.
+
+2. **String Length**: Device names are limited to 63 characters maximum.
+
+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.
+
+4. **Audio Levels**: Keep audio levels reasonable to prevent distortion. Start with conservative values and adjust as needed.
+
+5. **Preemphasis**: Use 50µs for European broadcast standards, 75µs for North American standards.
+
+## Troubleshooting
+
+- **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