DocsReference
Privacy and technical details
What the server does and doesn’t do, where your data is kept, network requirements and technical values.
Where your recordings are kept
Your recordings are not stored on any server. The sound is first written to the computer of the person recording, then, when the recording ends, moved directly to the host’s computer and merged there.
Mixapod contains no usage statistics or ad trackers.
What the server does
Mixapod’s server (mixapod.heworx.com) only brings people together:
| Job | Description |
|---|---|
| Sessions | Links the invite code to the session and keeps track of who is in the session |
| Connection setup | Passes between two computers the information they need to connect directly |
| Shared clock | Provides time information so the recording starts and stops at the same moment for everyone |
| Contacts and calls | Relays the online status of people who have added each other, and calls |
| Mixapod numbers | Keeps track of which number belongs to which computer |
| Relay | Passes encrypted traffic on networks that can’t connect directly |
| Updates | Provides new version information and the installer |
Online status, missed call notifications (24 hours) and call limit counters are kept only in the server’s memory; they are erased when the server restarts. Display names and session codes are written to the server log.
What the server sees
To set up calls and sessions the server sees the following; it never sees sound, recordings or files:
- who is in which session, display names, whether someone is muted, the session title, when recording starts and stops,
- who called whom, Mixapod numbers and status messages,
- for Who can call me and online visibility: the numbers in your contacts and the numbers you have blocked.
The connection to the server is encrypted with HTTPS / WSS; nobody on the network can read this information.
Sound and files travel encrypted
Live call audio, soundpad sounds and recording files are encrypted by WebRTC: audio with DTLS-SRTP, files with DTLS. The encryption keys are created on the two computers; the server doesn’t see them. Even when a direct connection can’t be made and the relay server is used, the server only passes encrypted packets along; it can’t see the content and doesn’t store it.
The two computers send each other their key fingerprints through the Mixapod server. If someone stepped in on the server and swapped them, you could tell: the lock on each person’s card in the lobby shows a 20-digit safety code computed from both fingerprints. If you both see the same code, nobody is in between. The code has 20 digits because a short one could be faked by generating new keys until it matched.
So that two computers can find each other, Mixapod uses Google’s public STUN server in addition to its own server. The STUN server only sees your computer’s public IP address; it sees no sound or content.
Information kept for numbers
For each number, the server keeps only the following: the number, a hash of the secret key on your computer (not the key itself), a hash of the recovery code, and the time the number was issued and last seen. The secret key stays only on your computer.
Files kept on your computer
| What | Where |
|---|---|
| Recordings and merged files | Documents\Mixapod |
| Settings | %APPDATA%\Mixapod\settings.json |
| Contacts and calls | %APPDATA%\Mixapod\contacts.json, calls.json |
| Soundpad settings, sounds and icons | %APPDATA%\Mixapod\pads.json, pads\ |
| Preamp settings and your presets | %APPDATA%\Mixapod\preamp.json |
| Secret key of your Mixapod number | %APPDATA%\Mixapod\identity.json |
| Log | %APPDATA%\Mixapod\logs\main.log |
| Downloaded updates | Temporary folder, mixapod-update |
There are no accounts; no e-mail address, phone number or password is asked for.
Network requirements
| Connection | Port | What for |
|---|---|---|
mixapod.heworx.com | 443 (HTTPS / WSS) | Sessions, shared clock, contacts, numbers, updates |
| Direct WebRTC | UDP, variable | Live audio and file transfer |
| Relay (TURN) | 3478 UDP/TCP, 5349 TLS | When a direct connection can’t be made |
Most home and office networks need no extra setup. On corporate networks where UDP is blocked, the connection is made through the relay.
Technical values
| Value | |
|---|---|
| Recording | WAV, 48 kHz, 24-bit, mono, per person |
| Session | 1 host + up to 4 guests |
| Recording start | On the shared clock, at the end of a 3-second countdown |
| Seat kept after a drop | 10 minutes |
| File transfer | 64 KB chunks, resumes where it left off, SHA-256 verification |
| Speed correction | Up to ±1000 ppm |
| Voice balancing | −20 LUFS per person (ITU-R BS.1770) |
| Mix | Stereo, −16 LUFS, limiter −1 dBFS (5 ms lookahead) |
| Output | Stereo WAV 48 kHz 24-bit + MP3 192 kbps |
| Production | MP3 128 / 96 / 56 kbps, WAV; 44.1 / 48 kHz |
| Preamp latency | 119 samples (2.5 ms), compensated in the recording |
| VU meter | IEC 60268-17 ballistics, 0 VU = −18 dBFS |
| Call ring time | 60 seconds; an invite to an offline contact waits 10 minutes |
| Update check | 8 seconds after launch, then every 4 hours |