scale(recording, gain) doesn't update "gain_to_uV" and "offset_to_uV" in BaseRecording

I noticed that the methods in spikeinterface/preprocessing/normalize_scale.py don't appear to keep track of a change to the gain or offset.

I understand that for most use cases it might not be useful to keep track of a change in offset (e.g., demeaning traces), but for scaling the traces, I think it would be helpful to keep track of the gain so that return_scaled=True is consistent.

For now the following code works for me:

rec_scaled = si.scale(recording, gain=scale_factor, offset=0.0)

new_gain   = recording.get_channel_gains()/scale_factor
rec_scaled .set_channel_gains(
    gains=new_gain, channel_ids=recording.get_channel_ids())

Interestingly, scale_to_uV() does update the gain and offset, so return_scaled=True is consistent:

def scale_to_uV(recording: BasePreprocessor) -> BasePreprocessor:
    [...]

    scaled_to_uV_recording.set_channel_gains(gains=1.0)
    scaled_to_uV_recording.set_channel_offsets(offsets=0.0)

    return scaled_to_uV_recording

https://github.com/SpikeInterface/spikeinterface/blob/cb83327c192f16d65698994f710c3c005384b4df/src/spikeinterface/preprocessing/scale.py#L37C1-L38C60

Nevertheless, I think it would be helpful if BaseRecording was able to keep track of how the data was scaled using any of the methods in normalize_scale.py.

Where I think scaling is useful, and where I plan to use it, is to utilize more of the int16 bit range.

The ADC in Neuropixels 1.0 is 10-bits, and Neuropixels 2.0 is 12-bits. This means you can scale NP1 by 64x and NP2 by 16x with no worries of clipping when casting back to int16.

Given that most pre-processing is done after casting to float32, but it makes sense to cast back to int16 before writing to disk, I think scaling after pre-processing but before casting back to int16 makes a lot of sense.

What are your toughts?

Start in spikeinterface/preprocessing/normalize_scale.py and compare the scaling methods with scale_to_uV() in scale.py, which updates channel gains and offsets. Trace how BaseRecording exposes get_channel_gains(), set_channel_gains(), and return_scaled=True. Done means scaling preserves consistent gain and offset metadata so returned scaled traces reflect the transformation.