Widen or narrow the stereo image of a recording with the ffmpeg extrastereo filter on Windows,…

Guide ID: art_01M7CCWKV6V3TFA4PMYXK7107B

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Guide title

Widen or narrow the stereo image of a recording with the ffmpeg extrastereo filter on Windows, and check what it did: a script that measures the middle and the side before and after, the mono sum and the peak

Coverage

Making a two-channel recording wider or narrower with a command line tool, and checking the result with numbers. A PowerShell script runs the ffmpeg extrastereo filter, writes a WAV or FLAC, then reports the level of the left, right, middle and side parts before and after, the mono-sum change and the peak. Generated noise and tones with a known side show what each width does.

Example

On generated noise the middle stayed put while the side followed the width: twice the width raised it 6 dB, half lowered it 6 dB, zero removed it. A sound in one channel leaked into the other as an inverted copy. The filter cut its own output at full scale, which also changed the middle. Nothing was listened to.

Useful starting points

• Print the plan first; it shows the side change in dB before anything is written.
• Lower the file's level before widening when the peak line warns.
• Fold the result to mono and listen yourself; the numbers say the middle stayed put, but nothing in the guide was listened to.