DocsSessions and recording

Transfer and merge

How the files move to the host once the recording ends, and the details of the process that merges the voices into one file.

Transfer#

When the recording stops, each guest sends their own file to the host.

• The file goes directly from computer to computer; it is not stored on the Mixapod server. On networks where a direct connection can’t be made, the encrypted traffic passes through a relay server, and it still isn’t stored.
• A ring that fills up with a percentage appears on the guest’s screen; when it’s done, it says Uploaded.
• The file is sent in 64 KB chunks. If the connection drops, the transfer resumes where it left off instead of starting over.
• The received file is verified with SHA-256: the file that reaches the host is bit-for-bit identical to the guest’s recording. If it doesn’t match, the guest sends the file again.

The host’s Mixapod requests missing files on its own: when collecting starts and when a guest reconnects. When everything has arrived, the merge starts on its own.

Merge#

When everyone’s file has arrived, the host’s computer starts merging. The stages are shown on screen with a progress bar.

1. Alignment#

The start frame of each file on the shared clock is known; the files are placed on the timeline with sub-millisecond precision. Several files from someone who joined the recording midway are also put in their right places.

2. Sound card speed correction#

Even when two sound cards both say “48 kHz”, their clocks don’t run at exactly the same speed; over a one-hour recording the difference can add up to seconds. Mixapod measures each recording’s real speed and corrects differences up to ±1000 ppm, so the voices still line up at the end of the episode. The correction is applied to people whose recording consists of a single file.

3. Voice balancing#

Each person’s voice is brought to −20 LUFS using ITU-R BS.1770 measurement; gain is raised by at most +18 dB and lowered by at most −24 dB. Someone who talks loudly and someone who talks quietly are heard at the same level.

4. Stereo mix#

The voices are spread slightly across the stereo field in the order people joined the session, which makes it easier for listeners to tell who is speaking. The spread is kept narrow so it isn’t distracting on headphones.

Soundpad effects go into the mix as a separate Effects track, in the center and at the level they were played; they are not balanced.

5. Level and limiter#

The mix is brought to podcast level, −16 LUFS; a limiter with 5 ms of lookahead keeps the peak level below −1 dBFS.

Output files#

In the take folder (Documents\Mixapod\<date> <episode title>\Take 1\):

On the Recording ready screen you can listen to the merged recording, open the tracks in Studio with Edit in Studio, go to the files with Show in folder, move on to production with Add to production, or record a new take with Back to lobby. You can open files with Open and move them to the Recycle Bin with the trash can icon.

My recordings#

No file is deleted when the merge is done: the raw recordings, the separate tracks and the mix stay in the recording’s folder. The take folder also gets a mixapod-take.json with the recording’s title, length, people and tracks.

My recordings in the sidebar, or File › My recordings, opens a panel on the right. Every merged take is listed, newest first. Each recording has:

• Play: Plays the mix inside the panel.
• Edit: Opens the recording in Studio.
• Add to production: Sends the mix to production.
• Show in folder: Shows the files in File Explorer.
• Delete: After asking, moves the take’s whole folder (mix, separate tracks, raw recordings) to the Recycle Bin.

With more than three recordings a search box appears for titles and people. Open folder at the top of the panel opens the recordings folder in File Explorer.