U-Sync Plugin Rounding Error using Ableton Link

[Sek0ps]

U-Sync Plugin Rounding Error using Ableton Link

Short description of the issue:
U-SYNC plugin displays a different BPM from Nome/Bitwig when Ableton Link is enabled in Bitwig.

Setup (devices connected and how):
I’m experimenting with using Nome II as the master clock for Bitwig via U-SYNC, while also wanting Bitwig to synchronize downstream devices — in particular a Denon SC6000 DJ deck, which supports Ableton Link.

The intended setup is:
Nome II → U-SYNC → Bitwig → Ableton Link → SC6000
Nome II is connected to the Mac via USB-C. U-SYNC plugin and daemon are running, with the Sim’n Tonic Bitwig controller configured using Nome II DAW Control as input and Nome II Commands as output.

Steps to Reproduce:
Run Bitwig with the U-SYNC plugin and daemon, with Bitwig Sync set to Off.
Nome II and Bitwig correctly show the same tempo, including two decimal places.
Enable Ableton Link as Bitwig’s sync method.
Change the tempo from the Nome II.

Expected Behavior:
Nome II remains the master via U-SYNC, Bitwig follows it, and Bitwig can participate in an Ableton Link session so that downstream Link devices can synchronize to the Nome-derived timing.
I would also expect the U-SYNC plugin BPM display to continue reflecting the Nome/Bitwig tempo correctly.

Actual Behavior:
Synchronization itself appears to work perfectly. Nome continues to control Bitwig's tempo and Bitwig successfully transmits the resulting timing over Ableton Link.
However, the U-SYNC plugin BPM display becomes inconsistent.
For example:

Nome actual tempo: 137.99 BPM
Bitwig: 138.0 BPM
U-SYNC plugin: 137 BPM

At 138.01 BPM:
Bitwig: 138.0 BPM
U-SYNC plugin: 137.0 BPM

Despite this discrepancy, everything appears to remain correctly synchronized.
Is this simply a display/rounding issue in U-SYNC when Bitwig's Ableton Link sync is enabled, or could it indicate an underlying synchronization issue?

Nome generation (I or II) and Firmware version:
Nome II
Firmware: [5.2]
U-Sync 1.4.1
Bitwig 6.1 Beta 6

More info:
The reason for enabling Ableton Link is specifically to retain Nome II → U-SYNC → Bitwig as the master timing path, while using Bitwig's Link implementation to distribute that timing to Link-capable downstream equipment such as the Denon SC6000.

[simntonic]

Hi

Thank you for the nice and detailed report - much appreciated!

We have not tested U-SYNC while Ableton Link is enabled (in any DAW), so it is not an officially supported configuration.

The list of different configurations one can use in a DAW is already tremendous, combine that with the many DAWs we support, soon two OSes, different audio interfaces, running at different sample rates, buffer sizes, and even the 3 devices supported by U-SYNC... The test matrix is huge, so we have to set limits unfortunately.

The good news is that it looks like it is working except that minor BPM issue?

Link is widely used though, especially to sync multiple DAWs, so we will do what we can to add it to the supported configuration eventually.

Thank you
Simon

[Sek0ps]

Hi Simon,

Yes, that's right; so far it appears to be a purely cosmetic issue in the plugin BPM readout as far as I can tell, with downstream Link clients responding to the correct BPM.