Podcast editing online: tracks, loudness and chapters

Apple Podcasts asks for −16 LUFS with a true peak no higher than −1 dBFS; for a mono file the accepted target is −19 LUFS, which sounds equally loud. The editor mixes the episode, measures it per ITU-R BS.1770 and only then sets the gain, and once the file is built it shows what came out: the loudness and the peak of the finished episode. The target can be changed to −14, −18 or −23 LUFS, or switched off.

The “Sync the tracks” button looks for sound the recordings share — a conversation in one room, a clap before the start, a voice coming from the speakers — and shifts the tracks to within a millisecond. On recordings of four minutes and longer it also finds how far the devices' clocks drift and corrects the track's speed. If everyone wore headphones and there is no shared sound, the editor says so and moves nothing: then you move the track by hand while holding Ctrl.

Chapters are written into the MP3 as ID3 CHAP and CTOC frames — Apple Podcasts and players such as Overcast and Pocket Casts display them. Spotify and YouTube take chapters from the episode description: “Copy timestamps” gives them in the expected form — the first line at 00:00, one line per chapter; Spotify wants at least three. For RSS with the Podcasting 2.0 tag there is a JSON file. Chapters are not written into WAV, FLAC or M4A.

The speakers are recorded separately, and if a piece is cut from only one of them, their answers slide out of step with the questions. So “Cut” removes the stretch of time from everyone and closes the gap. “Silence” is for one person's sound: a cough or a knock leaves their track, and the length of the episode does not change.

When two people sit in one room, each microphone also hears the neighbor — quieter and late, which gives an echo in the mix. The editor compares the tracks: where a recording is clearly quieter than the neighboring one while that neighbor speaks, it is turned down by up to 12 dB. Simultaneous speech and quiet remarks are left alone. Recordings from different rooms do not need the switch.