6 min read
Merging audio files: joining end to end versus combining channels
Combining channels and concatenating clips are opposite operations. Picking the wrong one is why your merged file sounds like mush.
Ask three people to merge audio files and you will get three results. One appends the clips into a longer file, one stacks the tracks into a multichannel file, and one sums everything into a single mono track. Only the second is what a post workflow usually wants.
Combining channels: mono stems into one file
This is the standard film case. A recorder wrote separate mono files for boom, lav A and lav B; the edit wants them as one multichannel WAV with the tracks in a known order. Every file must share the same sample rate, bit depth and length, and the channel order must be documented.
- Same sample rate: convert first if one file is 44.1 kHz.
- Same bit depth: mixing 16 and 24 bit sources means one gets converted anyway, so decide deliberately.
- Same start point: files that do not share a timecode origin must be aligned before merging.
- Named tracks: write the track names so the editor sees BOOM, not channel 2.
Summing: when merging means mixing
Summing several tracks into one mono file adds their levels. Two identical signals sum 6 dB louder, and imperfectly aligned copies of the same source produce comb filtering rather than a fuller sound. Sum only when you actually want a mixdown, and set per track gain before you do.
Joining end to end
Concatenation is for splitting a long recording that got interrupted, or rejoining a card that spanned files at the 4 GB limit. The requirement is identical format on both sides; anything else creates a click or a speed change at the join.
Doing it without uploading anything
The mono merger on this site accepts up to twelve mono files, lets you rename each track and set its gain, and writes a single multichannel WAV or AIFF at the sample rate and bit depth you pick. Everything happens in the browser, so unreleased material never leaves your machine.