On Fri, Oct 25, 2013 at 2:34 PM, Pierre Haessig <pierre.haes...@crans.org>wrote:
> Hi,
>
> Le 22/10/2013 19:14, Todd a écrit :
>
> Thanks for the feedback. I agree that your documentation does make clear
>> the distinction between "phase" and "angle" and that it has a consistency.
>> I just feel that this distinction does not exist "outside" ...
>>
>> But beyond this question of phase vs. angle, I must say I don't see that
>> big a use case for phase/angle spectrums[*] (as opposed to magnitude which
>> are much used).
>>
>
> I personally use phase and angle spectrums a huge amount. In signal
> processing it is extremely important. It is a critical component in
> acoustics. It is also used a lot to separate out signals that have been
> mixed together. Knowing the phases of signals can also be very important
> in certain optics applications and for radio signals and RADAR. Changes in
> the phase spectrum over time (like you would get from a phase spectrogram)
> is important for doppler analysis both with optical and acoustic signals.
>
> Also, from an educational perspective, anyone taking a digital signal
> processing course will need to produce magnitude/phase plots, probably both
> with and without wrapping (since any decent digital signal processing
> course will teach you about the pitfalls that occur due to phase
> wrapping). So this will make matplotlib much more useful for such courses.
>
>
>> Also, in many cases, "spectrum" is synonymous with spectral density,
>> which implies "magnitude". In the end I wonder whether the notion of phase
>> even makes sense for a spectrogram ?
>>
>
> Yes, particularly electrical engineering. But there are many other
> fields where spectral density is rarely used, and where more "ordinary"
> magnitude and phase plots are the norm, as I explained in the previous
> paragraphs.
>
> Thanks for dealing with my ignorance. It's true that I have a biased view
> on these frequency functions, because I mostly deal with random signals
> these days.
>
> In fact I'd like to understand a bit more how phase spectorgram works.
> Since the signal must be cut into chunks to make the plot along time, how
> is the phase computations "synchronised", that is, how does it use a common
> time reference. (because I would imagine that otherwise the phase would
> make "jumps" between each window frame). Do you have a pointer for how this
> is solved ? (or is this problem just non-existing?).
>
> best,
> Pierre
>
This could certainly be an issue, and no it isn't dealt with (nor am I
aware of a way it could be dealt with).
There are really several different questions here.
First, is it worthwhile having 1-D phase and angle spectrums
(phase_spectrum and angle_spectrum). I would argue that this is definitely
the case, as I already explained.
Second, is it worthwhile adding these to specgram? Frankly. probably not.
They have some robustness issues.
Third, given that implementing phase_spectrum and angle_spectrum
automatically gets us phase and angle specgrams, and that it would actually
take more code to turn them off than to leave them in, is there any reason
to explicitly disable these plot type? I would say no. It is a tool. It
may not be useful to very many people, and the people who do use it may
need to be careful to use it properly. But since we get it for free
anyway, I don't see a good reason to put in the extra code to remove
functionality that may be useful to someone but hurts no one.
------------------------------------------------------------------------------
October Webinars: Code for Performance
Free Intel webinars can help you accelerate application performance.
Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from
the latest Intel processors and coprocessors. See abstracts and register >
http://pubads.g.doubleclick.net/gampad/clk?id=60135991&iu=/4140/ostg.clktrk
_______________________________________________
Matplotlib-devel mailing list
Matplotlib-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
