Fabian Brinkmann

Yes, would be nice to have. Let's maybe discuss before implementing if this should go into pyfar or somewhere else.

> I made `Filter` an `ABC` but now the tests are failing because `Filter` can no longer be instantiated. I cannot think of a use case of instantiating a `Filter`...

I think we discussed this quite a while ago when designing the Signal calsses and decided against it. We also thought about the possibility to have a nested coordinates object...

> It does not support multidimensional labels, doesn't it? Just one label for all channels. you can do `label=('ch 1', 'ch 2')` and so on. Since we are flattening multidimensional...

I took a look. The current implementation requires equidistant frequencies, but the therory behind this does not rely on this assumption. So it could be implemented but would require some...

I agree with the suggestions, but have two comments - I would keep the naming convention, i.e., use `nominal_fractional_octave_frequencies` instead of `fractional_frequencies_nominal` - The *exact* function should return the cut-off...

We decided to do this as suggested but: - use `num_fractions` everywhere - and use `fractional_ovtave_frequencies_nominal` and `fractional_ovtave_frequencies_exact`

@h-chmeruk are you also working on deprecating the old [pyfar.dsp.filter.fractional_octave_frequencies](https://pyfar.readthedocs.io/en/stable/modules/pyfar.dsp.filter.html#pyfar.dsp.filter.fractional_octave_frequencies)? I could take care of this, in case you're not.

@ahms5 I'll do this after #829 is complete