Full Explanation of the Audio Equalizer + BassBoost + Virtualizer + Presets + Visualizer (B4XPages + ExoPlayer)
This code implements a complete
audio processing page using B4XPages. It includes:
- SimpleExoPlayer audio playback
- Android AudioFX Equalizer (5 bands)
- BassBoost
- Virtualizer
- Preset system (Pop, Rock, Techno, Vocal Booster, etc.)
- Winamp‑style visualizer simulation
- Automatic persistence using KeyValueStore
- Dynamic initialization based on the audio session ID
It is designed to be easy to integrate, modify, and extend.
1. Page Initialization
In B4XPage_Created, the code:
- loads the layout
- initializes KeyValueStore
- configures the ComboBox
- groups the 5 equalizer sliders into a list
- assigns each slider a Tag representing its band index
- initializes the visualizer arrays
- starts a timer for the visualizer (≈30 FPS)
- initializes ExoPlayer and prepares a sample MP3
This creates the foundation for the equalizer and visualizer.
2. Dynamic Equalizer Initialization
Android’s audio effects (Equalizer, BassBoost, Virtualizer)
must be created using the audio session ID of the player.
When ExoPlayer is ready:
[CODE lang="b4x" title="B4A"]Dim AudioSessionId As Int = nativePlayer.RunMethod("getAudioSessionId", Null)[/CODE]
If the ID is valid, the code initializes:
[CODE lang="b4x" title="B4A"]EQ.InitializeNewInstance("android.media.audiofx.Equalizer", Array(0, SessionId))
BassBoost.InitializeNewInstance("android.media.audiofx.BassBoost", Array(0, SessionId))
Virtualizer.InitializeNewInstance("android.media.audiofx.Virtualizer", Array(0, SessionId))[/CODE]
Then
:
- retrieves the min/max band levels
- configures each slider’s range
- restores saved values from KeyValueStore
- applies the saved equalizer settings
This ensures the equalizer is fully synchronized with the audio engine.
3. Equalizer Sliders
Each equalizer slider has a Tag containing its band index.
When a slider changes:
[CODE lang="b4x" title="B4A"]Dim BandIndex As Int = sb.Tag
Dim TargetMilliBels As Short = Value + EQMinLevel
EQ.RunMethod("setBandLevel", Array(AsShort(BandIndex), TargetMilliBels))[/CODE]
The value is also saved:
[CODE lang="b4x" title="B4A"]kvs.Put("Band_" & BandIndex, Value)[/CODE]
This makes the equalizer responsive and persistent.
BassBoost & Virtualizer
These effects use the same pattern:
[CODE lang="b4x" title="B4A"]BassBoost.RunMethod("setStrength", Array(AsShort(Value)))
Virtualizer.RunMethod("setStrength", Array(AsShort(Value)))[/CODE]
Both values are saved in KeyValueStore.
5. Preset System
The ComboBox contains several audio profiles:
- Flat
- Pop
- Rock
- Techno / Dance
- Vocal Booster
Each preset defines:
- 5 equalizer band values
- BassBoost strength
- Virtualizer strength
The preset is applied using:
[CODE lang="b4x" title="B4A"]EQ.RunMethod("setBandLevel", Array(AsShort(i), AsShort(GainMilliBels)))
sb.Value = SliderValue[/CODE]
This updates both the audio engine and the UI.
6. Winamp‑Style Visualizer
The visualizer is a
simulation, not a real FFT. It uses:
- 32 bars
- random values influenced by equalizer energy
- peak‑hold effect
- decay over time
- a timer running at ~30 FPS
Each timer tick:
- Updates bar values
- Updates peak values
- Draws bars and peaks on a B4XCanvas
- Clears and redraws the panel
This produces a smooth, animated visualizer similar to classic Winamp skins.
7. Automatic Persistence (KeyValueStore)
All user settings are saved:
- equalizer band levels
- BassBoost strength
- Virtualizer strength
On startup, the values are restored and applied automatically.
This makes the audio page behave like a real equalizer app.
8. Summary for B4X Developers
This code demonstrates:
- how to use ExoPlayer with B4XPages
- how to initialize Android AudioFX correctly
- how to build a multi‑band equalizer
- how to implement BassBoost and Virtualizer
- how to create a preset system
- how to draw a custom visualizer
- how to persist settings with KeyValueStore
It can be used as:
- a base for a full audio player
- a learning example for AudioFX
- a visualizer demo
- an equalizer module for existing apps
Required libraries
Have fun
