Network traffic: X32-Mix vs Mixing Station
Some users reported a delay and lag with the X32-Mix iPad app, so I wanted to investigate the differences in network communication between the two apps. In the following discussion, the X32-Mix iPad app is simply referred to as "X32-Mix".
Here are some quick facts about the network protocol used by the X32 (this will be the same for both apps):
- OSC (Open Sound Control) send via UDP
- UDP is not connection based, nor does it guarantee that all packets are delivered.
- OSC data structure:
- Path string: This indicates what content is in the package. Example: /ch/01/mix/level
- Value string: Information about the type and order of the values in the OSC message
- Value(s): Values attached to the OSC message. (Numbers, Text, etc.)
Keeping data in sync
One key function of a remote app is to show the current values of the console. To achieve this, the data in the app and the data in the console need to stay in sync. There are two different methods to get data from the X32:
- Polling (X32-Mix): The app sends a
/subscribecommand to the X32. The X32 then sends the requested value every 50 ms for the next 10 seconds. The 10 second timeout can be halted by sending the same command again. - Events (Mixing Station): The app sends a
/xremotecommand to the X32. The X32 responds with all value changes that occur in the next 10 seconds.
As you may have noticed the "event" mechanism only sends data when a value changes. This saves a lot of data! This is also the reason why Mixing Station requires a sync when connecting and X32-Mix doesn't because every 50 ms it retrieves all values that are currently visible.
Measurements
| View | X32-Mix iPad receive | X32-Mix iPad send | Mixing Station receive | Mixing Station send |
|---|---|---|---|---|
| Sync | N/A | N/A | ~65 | ~50 |
| Mixer Ch 1-8 | < 1 | ~44 | < 1 | ~21 |
| Change to Ch9-8 | ~20 | ~44 | ~5 | ~34 |
| LR PEQ | < 1 | ~28 | < 1 | ~7 |
All values in kByte/s
For better comparison here are some differences regarding the data requested by the apps:
| Feature | X32-Mix iPad | Mixing Station |
|---|---|---|
| RTA data | No | Yes |
| GR meters in mixer view | No | Yes |
Why the lag?
You still may wonder "why does the iPad app lag sometimes?" The data that is displayed on screen is not cached inside the app, it's the last data that was received from the X32 via the network. This means, when you drag the fader on the screen with your finger, the fader shown on the screen only moves when the value that is sent back from the X32 to X32-Mix is updated. On a regular network this isn't a issue, but we're talking about a WiFi network that has to transfer a lot of small packets in both directions. Depending on the WiFi-Router, some packets will get lost and the average latency will increase. Also when you change the view in X32-Mix it has to wait until all required values arrive before it can show any content as the app has no local cache to store old values.
How does Mixing Station stay in sync?
As you may have noticed, UDP may drop some packages. If a value has been changed (like a mute button) and the packet gets lost, the app will not be notified about the change. To overcome this issue, Mixing Station periodically syncs all required values in the background. This also means that if a package gets lost, the app might be out of sync for up to 1 minute.