Audio Channel Converter — Upmix & Downmix Surround Sound Online
Convert between stereo and surround sound formats instantly in your browser
Whether you need to create a 5.1 surround mix from stereo music for your home theater, convert a 7.1 movie soundtrack to stereo for headphones, or prepare mono audio for older devices — this tool handles all channel conversions. Three upmix algorithms let you choose between speed, quality, and cinematic depth. Everything runs locally in your browser using FFmpeg WebAssembly — your files never leave your device.
Key Features
- Upmix stereo to 5.1 (6 channels) or 7.1 (8 channels) surround sound
- Three upmix algorithms: Simple Copy, Matrix Decode (Pro Logic II style), and Enhanced with bass management
- Downmix 5.1/7.1 surround to stereo or mono with professional mixing coefficients
- Auto-detect input channel count and validate conversion compatibility
- Output to FLAC, WAV, or OGG for multichannel; plus MP3 for stereo/mono
- LFE subwoofer channel with proper 120 Hz lowpass filter (Enhanced mode)
- Surround channel delay for increased depth perception (Enhanced mode)
- 100% browser-based processing — no file uploads, no server, no registration
How to Convert Audio Channels
- Choose your conversion direction: Upmix (stereo → surround) or Downmix (surround → stereo/mono)
- Upload your audio file — MP3, WAV, FLAC, OGG, AAC, AC3, and more are supported
- The tool auto-detects the number of channels in your file
- For upmix: select target (5.1 or 7.1), choose algorithm (Simple, Matrix, or Enhanced), and pick output format
- For downmix: select target (Stereo or Mono) and output format
- Click "Convert" and wait for processing to complete
- Download your converted file
Frequently Asked Questions
Can I create real surround sound from stereo?
True surround requires recording with multiple microphones. However, Matrix Decode extracts genuine spatial information from stereo — the L-R difference signal contains reverb, ambience, and spatial effects that naturally belong in surround speakers. The result is noticeably more immersive than plain stereo, especially for well-mixed music and movie soundtracks.
Which upmix algorithm should I use?
Matrix Decode is the best balance of quality and compatibility. Enhanced adds proper bass management (LFE with 120 Hz lowpass) and surround delay for a more cinematic feel — ideal for home theater. Simple is fastest but just copies channels without spatial processing.
Why can't I save surround audio as MP3?
The MP3 specification only supports up to 2 channels (stereo). For multichannel audio, use FLAC (lossless, best quality), WAV (lossless, larger files), or OGG Vorbis (lossy but compact). All three fully support 5.1 and 7.1 channel layouts.
Will downmixing 5.1 to stereo lose quality?
Downmixing uses standardized mixing coefficients (ISO/IEC 13818-7) to combine all channels into stereo. You don't lose audio content — the center, surrounds, and LFE are blended into L/R at calibrated levels. The result sounds natural on headphones and stereo speakers.
What is the LFE channel?
LFE stands for Low Frequency Effects — it's the ".1" in 5.1 and 7.1. It carries only bass frequencies (below 120 Hz) intended for a subwoofer. In Enhanced upmix mode, bass is separated from the main mix using a lowpass filter and routed to the LFE channel.
Does this work with video files?
This tool processes audio files only. To convert channels in video files, extract the audio track first, convert it here, then remux it back into the video using a video editor or FFmpeg.
Is my file uploaded to a server?
No. All processing happens locally in your browser using FFmpeg WebAssembly technology. Your files never leave your device — nothing is uploaded, stored, or transmitted.
Why Use This Channel Converter
No software to install, no registration, no file size limits that matter for audio. Process files of any length entirely in your browser. Supports all major audio formats for both input and output. Three upmix algorithms from simple to cinematic. Professional downmix coefficients matching hardware receivers. Private and secure — your audio stays on your device.
