[pulseaudio-discuss] R: New equalizer module (module-eqpro-sink), some questions

[Alexander E. Patrakov]

пн, 8 апр. 2019 г. в 12:27, Georg Chini <georg at chini.tk>:
>
> On 05.04.19 13:29, Tanu Kaskinen wrote:
> > On Tue, 2019-04-02 at 20:28 +0200, Georg Chini wrote:
> >> On 06.11.18 22:14, Andrea A wrote:
> >>> Thanks a lot for the reply
> >>>
> >>>> If the preset files are expected to be shared between users, then the
> >>> database.h stuff isn't good, because different users can have their
> >>> pulseaudio configured with different database formats. I like the "ini-
> >>> style" configuration file style that pulseaudio uses for .conf files.
> >>> There are no helpers for writing those files, though, but that's
> >>> probably not a big issue.
> >>>
> >>> I can write a parser for ini-style file however since PA is
> >>> multiplatform I need some information about how to store user and
> >>> system settings. System settings can be hardcoded at least, but the
> >>> directory of user config depends on the platform I think.
> >>>
> >>>> Iwould love to have the equalizer as a LADSPA plugin
> >>> My fear is that a LADSPA plugin will be too hard to use for a lot of
> >>> desktop users. I think that a GNU desktop user would like to have a
> >>> fully working audio equalizer in his distribution and PA is default in
> >>> almost all GNU distributions. Configuring a LADSPA plugin may be hard
> >>> and boring for the average user and GNU will continue to don't have a
> >>> standard equalizer. Beyond the issues you've already listed.
> >>>
> >>>> It's not very uncommon that some core
> >>> change requires changes in all sinks, so even if the module is perfect
> >>> and doesn't require maintenance in form of bug fixes, there are other
> >>> kinds of real maintenance costs.
> >>>
> >>> As far as I know the actual equalizer is deprecated so if this mine
> >>> equalizer will be adequate I think that the actual can be substitute
> >>> and the number of modules to maintain will not change.
> >>>
> >>> Andrea993
> >>>
> >>>
> >> Hi Andrea,
> >>
> >>
> >> maybe there is a chance now to have your equalizer included as a module.
> >> The messaging API patches
> >> should have their final form (at least I do not think the public
> >> functions will change anymore) and today
> >> I submitted a patch series that consolidates the code of the current
> >> virtual sinks and moves the common
> >> code to a separate file. Using the common code should significantly
> >> reduce the maintenance cost of an
> >> additional sink.
> >>
> >> So if you are still interested to have it included, at least I would
> >> welcome a new patch.
> >>
> >>
> >> Arun, Tanu, what do you think?
> > I think it would anyway make sense to make one or more LADSPA plugins
> > out of the equalizer code (I say one or more, because of the lack of
> > parametrization support in LADSPA). That way the equalizer would be
> > available also to other software than just PulseAudio (I'm thinking
> > PipeWire in particular).
> >
> > If a suitable LADSPA plugin existed, we might or might not still need a
> > separate equalizer module, but in any case we wouldn't need to maintain
> > the DSP code in PulseAudio. If there's some reason why module-ladspa-
> > sink isn't (and can't become) suitable for implementing the integration
> > in PulseAudio, then a specialized module is fine.
> >
> > I'm not saying that I'm dead against hosting the DSP code in
> > PulseAudio, but I'd certainly prefer not to.
> >
> It surely would make sense to have one or several  LADSPA
> plugins, but for me a good equalizer should be an integral
> part of pulseaudio. And as you say yourself, the full flexibility
> cannot be achieved by a single LADSPA plugin. The equalizer
> we are currently providing is buggy and completely unsupported.
> The new equalizer would at least be fully documented, so that
> it is possible to maintain. Additionally I agree with Andrea that
> handling LADSPA plugins is somewhat cumbersome. From a
> user point of view, a module is much easier to handle.

I have looked again at the paper, and have a DSP question.

The thesis starts with designing a shelf filter. That is, a filter
that contains a flat area at low frequencies, a flat area at high
frequencies (but with a different gain), and some transition in
between. Then, for some unknown reason, it is transformed into a
band-pass shelving filter. Then there is some talk how to "stitch"
together several band-pass shelving filters.

Why would one need to do this at all? I.e., why can't one just cascade
several shelf filters, designed according to the correct transition
frequencies, with the height of the shelf being the dB difference of
the desired gains of the neighboring bands?

-- 
Alexander E. Patrakov