---
title: Effects & Filters
description: Learn how to use audio effects and filters
---

## Overview

*flutter_soloud* provides various audio effects and filters that can be applied globally to all sounds or individually to specific sound sources.

**Note:** individual filters are not supported on the web platform.

## Available Filters

- `echo` - Echo/delay effect [SoLoud documentation](https://solhsa.com/soloud/echofilter.html)
- `freeverbFilter` - High quality reverb effect [SoLoud documentation](https://solhsa.com/soloud/freeverbfilter.html)
- `biquadResonant` - Multi-mode filter (lowpass, highpass, bandpass) [SoLoud documentation](https://solhsa.com/soloud/biquadfilter.html)
- `bassboost` - Low frequency enhancement [SoLoud documentation](https://solhsa.com/soloud/bassboostfilter.html)
- `flanger` - Classic modulation effect [SoLoud documentation](https://solhsa.com/soloud/flangerfilter.html)
- `waveShaper` - Audio distortion/wave shaping [SoLoud documentation](https://solhsa.com/soloud/waveshaperfilter.html)
- `lofi` - Bit depth and sample rate reduction [SoLoud documentation](https://solhsa.com/soloud/lofifilter.html)
- `robotize` - Voice modulation effect [SoLoud documentation](https://solhsa.com/soloud/robotizefilter.html)
- `equalizer` - Multi-band equalizer [flutter_soloud source](https://github.com/alnitak/flutter_soloud/blob/main/src/filters/parametric_eq_filter)
- `pitchShifter` - Change pitch without affecting speed [flutter_soloud source](https://github.com/alnitak/flutter_soloud/blob/main/src/filters/pitch_shift_filter.cpp#L16)
- `compressor` - Dynamic range compression [flutter_soloud source](https://github.com/alnitak/flutter_soloud/blob/main/src/filters/compressor.cpp#L24)
- `limiter` - Peak volume control [flutter_soloud source](https://github.com/alnitak/flutter_soloud/blob/main/src/filters/limiter.cpp#L20)

<Info>
- Individual filters for sounds are not supported on Web platform.
- *freeverb* supports only 2 channels. So using *freeverb* as global filter, the engine should be initializeded using the default 2 channels and when using it as sound filter it must be with 2 channels.
</Info>

## Global Filters

Apply filters to all audio output:

```dart
// Initialize SoLoud with filters
await SoLoud.instance.init();

// Access filters through the filters property
final filters = SoLoud.instance.filters;

// Activate an effect
filters.echoFilter.activate();

// Configure parameters
filters.echoFilter.delay.value = 0.2;
filters.echoFilter.decay.value = 0.7;
```

### Parameter Control

```dart
// Fade parameter over time
filters.echoFilter.delay.fadeFilterParameter(
  to: 0.5,
  time: Duration(milliseconds: 1000),
);

// Oscillate parameter
filters.echoFilter.decay.oscillateFilterParameter(
  from: 0.2,
  to: 0.8,
  time: Duration(milliseconds: 2000),
);
```

## Common Filter Examples

### Echo Effect

```dart
// Set up echo
filters.echoFilter.activate();
filters.echoFilter
  ..delay.value = 0.2    // 200ms delay
  ..decay.value = 0.7    // 70% decay
  ..filter.value = 1.0;  // No filtering
```

### Parametric Equalizer

```dart
// Enhance low frequencies
filters.parametricEqFilter
  ..stftWindowSize.value = 2048 //STFT window size parameter (32-4096, power of 2, default 1024)
  ..numBands.value = 64         // number of bands parameter (1-64, default 3)
  ..bandGain(0).value = 1       // gain parameter for a specific band
  ..bandGain(1).value = 0.5
  ..bandGain(2).value = 1.3;
```

### Bass Boost

```dart
// Enhance low frequencies
filters.bassboostFilter.activate();
filters.bassboostFilter
  ..boost.value = 2.0;   // Double bass
```

### Lo-Fi Effect

```dart
// Add retro sound quality
filters.lofiFilter.activate();
filters.lofiFilter
  ..sampleRate.value = 8000   // 8kHz sampling
  ..bitDepth.value = 4;       // 4-bit depth
```

### Reverb

```dart
// Add space/room effect
filters.freeverbFilter.activate();
filters.freeverbFilter
  ..roomSize.value = 0.8    // Large room
  ..damping.value = 0.5     // Medium damping
  ..width.value = 1.0;      // Full stereo width
```

## Dynamic Effects

Create evolving soundscapes:

```dart
// Start with normal reverb
filters.freeverbFilter.activate();
filters.freeverbFilter.roomSize.value = 0.5;

// Gradually increase room size
filters.freeverbFilter.roomSize.fadeFilterParameter(
  to: 0.9,
  time: Duration(seconds: 3),
);

// Oscillate damping
filters.freeverbFilter.damping.oscillateFilterParameter(
  from: 0.2,
  to: 0.8,
  time: Duration(milliseconds: 2000),
);
```

## Best Practices

- Use filters sparingly to avoid CPU overhead
- Be careful with feedback parameters in echo/reverb
- Consider mobile device performance
- Deactivate unused filters
- Use parameter fading for smooth transitions
- Test on various devices and platforms
- Monitor CPU usage when using multiple filters