Device clock drift depends on the setup¶

The drift of the SNUADC's and the BIS's timestamps against the recorder PC is largely set by the setup: knowing a recording's PC key (the serial ports of its four core devices) puts the SNUADC's drift within 3 ppm of its setup's median in 97% of cases and the BIS's in 83%, against 34% and 17% for the release's median. On the whole release's correction intervals the same test gives 71% and 60% (Identifying the recording setup of every case).

What it means¶

A drift quoted over all recordings (in the correction scan's cases, SNUADC medians −47 to −80 ppm by port, BIS 18 to 51 ppm) overstates the uncertainty for a recording whose setup is known, and understates how different two setups are.

What is done about it¶

Where a track has no whole tooth to measure its own rate, use its setup's rate (the stamp model already uses the port's typical rate for the SNUADC), with the setup's spread as its uncertainty; fall back to a coarser key, then to the release, only when the PC key is incomplete. The per-setup rates are listed on SNUADC step-mode drift and BIS drift against the recorder PC, and in the register on Recording setups.

Detail¶

Drift per case from Clock corrections in every file, grouped by the serial ports each recording's devices were attached to (groups with at least 5 cases; the register is on Recording setups). Share of cases within 3 ppm of their group's median:

One port is a weak key because Windows numbers ports per PC: the SNUADC was on COM4 in 2,824 recordings, on several PCs, and with six inferred units. The four ports together rarely repeat across PCs.

Evidence¶