Incorrect assumptions in `neuropixels_utils`

[billkarsh]

Various comments in neuropixels_utils.py regarding the number of ADCs on probes are wrong. Have not checked if code is also wrong.

[zm711]

Thanks for taking the time to look at the project, we always appreciate when people involved in the various tooling provide feedback. That being said it would be more helpful if you pointed out which assumptions are wrong so we can fix them. Here's a nifty article on how to write a good issue. And we always welcome PRs :)

[billkarsh]

Read your comments about how many ADCs there are on various probes, and how many channels there are per ADC. The comments are variously wrong and/or inconsistent. If the comments are confused the code is likely similar. I won't point to a particular part of code because you should review all associated code.

[billkarsh]

The operations are documented here: https://github.com/billkarsh/CatGT/blob/main/Build/Tool.cpp::FFT::init(), FFT::timeShiftChannel().

The mux tables are in the public probeTable repo: https://github.com/billkarsh/ProbeTable.

The description of the mux table is here: https://billkarsh.github.io/SpikeGLX/Sgl_help/Metadata_30.html#imec.

The mux table is organized as (nADC,nGrp)(grp)(grp)… Each (grp) are the (acquired) channel indices that are digitized together.

The shift amount delT(igrp) is the time difference between group-igrp and group-0. Group-0 does not need to be shifted.

delT(igrp) = igrp/(nGrp*sample_rate).

Note that for 2.0-like probes (that are full band only), nGrp should be used as is from the table. In these cases the multiplexer clock runs at rate nGrp*sample_rate. That is, nGrp sets of channels are digitized during each effective sample period (1/sample_rate).

However, for 1.0-like probes that have an AP and an LF band, the multiplexer runs at (nGrp+1) * ap_sample_rate. In all cases so far, nGrp=12. During each sample period, the multiplexer digitizes {nGrp=12 AP channel groups + 1 LF group}. The LF groups are the same groups as the AP groups in the table, however, it takes 12 AP sample periods to digitize all of the LF groups. That’s how the LF sample rate becomes exactly 1/12 of the AP sample rate.

So when doing a 1.0-like AP file, delT(igrp) = igrp/(13 * ap_sample_rate).
When doing an LF file, delT(igrp) = igrp/(12 * lf_sample_rate), as if this was single-band data.