Dual mono

A dual-mono file is a stereo file whose left and right channels are exactly the same — really a mono recording stored twice. The Media Manager finds these files, marks them in the Finder and converts them to mono without losing their metadata.

Why it matters

Dual-mono files are common: a mono source recorded on a stereo track, a mono instrument bounced as stereo, or files exported from tools that always write stereo. They cause small but real problems:

• Twice the disk space for the same audio — and twice the data for the DAW to read.
• Stereo tracks where you expect mono. A dual-mono clip needs a stereo track, so pan and plug-ins behave differently than on a mono track.
• Confusing mixes. The file looks like it has width, but doesn't. Collaborators can't tell without checking.

More background: dual mono explained.

1. Find dual-mono files

By default, the Media Manager analyzes stereo files automatically after scanning a folder. The Dual mono column then shows Yes, No or Yes (silent) for every stereo file (all values).

If automatic analysis is turned off in settings, or for files marked ?, choose Actions › Analyze Dual Mono. Select files first to analyze only those.

How detection works

The analysis is bit-exact: it compares every left sample with the matching right sample. A file is dual mono only if all of them are identical. There is no tolerance and no guessing — a single differing sample makes the file No.

• Files that differ are usually recognized within the first second, because the comparison stops at the first difference. Dual-mono files have to be read to the end.
• Files that are entirely silent are reported as Yes (silent). Check them before converting: an empty file may be a mistake worth deleting rather than converting.
• Only uncompressed (PCM) stereo WAV, AIFF and CAF files are analyzed. Mono and multichannel files, and compressed formats like MP3 and AAC, show –.

2. Review the results

Choose Show › Dual mono in the toolbar to list only the dual-mono files, or sort by the Dual mono column. Listen to a few with the preview before converting — especially files you didn't expect.

3. Tag them in the Finder (optional)

Choose Actions › Tag Dual-Mono Files to add a Finder tag — Red by default — to every dual-mono file. The tag shows in the Finder, in the Tags column, and in Finder searches. It is a good way to mark files for later without changing them, or to show a colleague which files are affected.

Change the tag name and color in settings. Tags are never written during scanning or analysis.

4. Convert to mono

1. Select the files to convert — or select nothing to convert all listed dual-mono files.
2. Choose Actions › Convert to Mono….
3. Check the list in the sheet. Each file shows Convert or Skip with a reason, the output file, and what happens to the original.
4. If some files haven't been analyzed yet, click Analyze … Files first.
5. Click Convert … Files.

The conversion runs one file at a time. Cancel finishes or rolls back the current file and skips the rest — you never end up with a half-converted file. When it is done, the sheet shows a result for every file; use Copy Log to keep a record, or Show in Finder.

Replace the original, or write a new file

Choose in settings what conversion produces:

Replaces the original (default)

The mono file takes the original's name and place, so sessions and folders that refer to it find the new file. The original stereo file is kept as a backup:

• As .bak next to the file (default) — Kick.wav is kept as Kick.wav.bak.
• In a subfolder — moved into Originals (name configurable) next to the file. That folder is skipped when scanning.
• In the Trash — recoverable until you empty the Trash.
• Don't keep it — no backup. This can't be undone.

Is saved as a new file

The original stays untouched and a mono copy is written next to it: Kick.wav → Kick_mono.wav. Files whose output already exists are skipped.

What the conversion keeps

Other tools convert by decoding and writing a brand-new file, and drop everything except the audio. The Media Manager rewrites only the audio data and the format description, and copies everything else as it is:

• Sample rate and bit depth — the audio is not resampled or dithered. The mono channel is the left channel, bit for bit.
• Broadcast Wave data, including the time reference that places the clip on the Pro Tools timeline.
• Markers (cue points and regions), RIFF INFO, iXML and other chunks in WAV files.
• Names, markers and application data in AIFF files; info and other chunks in CAF files.

For Broadcast Wave files, a line is added to the coding history describing the conversion (can be turned off in settings).

Finder tags after converting

With Tag files when converting on (default):

• the original (or its backup) gets the dual-mono tag — Red;
• the mono file gets the converted tag — Green — and keeps the original's other tags.

Why a file is skipped

Using converted files in your DAW

• When the original is replaced, the file keeps its name and location, so the DAW finds it. A stereo track that played the file now plays a mono file; move the clip to a mono track if you want mono processing.
• Because the Broadcast Wave time reference is kept, Spot to original time stamp in Pro Tools still places the mono clip exactly where the stereo one was.
• Keep the backups until you have checked the session. Then delete the .bak files or the Originals folder to reclaim the space.