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-   -   Pulseaudio Crossover Rack - multi-way crossover design & implementation with linux (https://www.diyaudio.com/forums/pc-based/330273-pulseaudio-crossover-rack-multi-crossover-design-implementation-linux.html)

Tfive 14th August 2019 10:46 AM

Yesterday I finally fixed my cross-compilation setup for the armhf versions of ladspa-t5-plugins, the LADSPA-plugins that do the DSP work in the background for pulseaudio crossover rack.

Before they were compiled in a arm emulator with the armv6 architecture. They are now cross-compiled for armv7, which should be more suitable for RPi versions >= 2, maybe even with some performance improvements. Please could somebody confirm that the plugins still work fine on a actual RPi? I checked them in a armv7-virt emulator but you never know, so some feedback from you guys would be cool!

Ivo 14th August 2019 11:28 AM

I will, but it will take a week or two. I am on vacation.

DarpMalone 14th August 2019 09:03 PM

Quote:

Originally Posted by Tfive (https://www.diyaudio.com/forums/pc-based/330273-pulseaudio-crossover-rack-multi-crossover-design-implementation-linux-post5883492.html#post5883492)
Yesterday I finally fixed my cross-compilation setup for the armhf versions of ladspa-t5-plugins, the LADSPA-plugins that do the DSP work in the background for pulseaudio crossover rack.

Before they were compiled in a arm emulator with the armv6 architecture. They are now cross-compiled for armv7, which should be more suitable for RPi versions >= 2, maybe even with some performance improvements. Please could somebody confirm that the plugins still work fine on a actual RPi? I checked them in a armv7-virt emulator but you never know, so some feedback from you guys would be cool!

They seem to be working fine in Raspbian Buster on the RasPi4. Is there anything specific that you need me to try?

Currently just running various LR4 filers as well as parametric EQ

Tfive 14th August 2019 09:26 PM

No, of they load fine when pressing the green "play" button that means the architecture is correct.

Thanks for the feedback.

DarpMalone 14th August 2019 10:05 PM

Hey Tfive, have you tried or are you aware of any compression plugins that work with paxor? like a configurable compressor/limiter that can be inserted post-LPF

Tfive 16th August 2019 09:55 AM

First of all some technical background: ATM I don't know of any way how to change parameters of LADSPA plugins after they were inserted into pulseaudio, so I had to roll my own API that each plugin I want to use has to implement (I asked on the pulseaudio mailing list but never received any reply to my question).

For this reason, at least at the moment, I cannot use any pre made plugins.

But there's another side to the story, there are literally dozens if not hundreds of different compressor/limiter plugins out there, if counting all the commercial ones too. So the first question to ask would be: "Why do you want to have a compressor in you chain in the first place? Which problem are you trying to solve?"

DarpMalone 16th August 2019 01:26 PM

I would use it between the subwoofer x-over (70Hz LPF) and the subwoofer output for speaker protection. With your EQ I'll add a 6-9dB boost @ say 40Hz to a small woofer, forcing it to play lower than it naturally could in a given enclosure. That signal will go to the compressor with a threshold set to activate @ maybe 70% of the woofers excursion limit... Now, with with a 3:1 compression ratio for example, once the woofer reaches the specified threshold it will only see 1dB of gain for every 3dB of overall gain allowing the system to "appear" to play much louder than it should with it's extended low frequency range.

DarpMalone 16th August 2019 02:12 PM

1 Attachment(s)
I'm using a little 4ch AdAU1701 DSP to do just what I described above in this boombox right now but I'd like to go 6ch and all active, rather than 4ch w/passive crossover. I can't seem to get the passive x-over to sound just right, plus the inductors add unnecessary weight.

Attachment 775645

Tfive 16th August 2019 08:35 PM

Quote:

Originally Posted by DarpMalone (https://www.diyaudio.com/forums/pc-based/330273-pulseaudio-crossover-rack-multi-crossover-design-implementation-linux-post5886000.html#post5886000)
I'm using a little 4ch AdAU1701 DSP to do just what I described above in this boombox right now but I'd like to go 6ch and all active, rather than 4ch w/passive crossover. I can't seem to get the passive x-over to sound just right, plus the inductors add unnecessary weight.

Attachment 775645

Man, go for it, and be the first to post that sweet "I did it with pulseaudio crossover rack" success story I'm still looking for :D That looks like a pretty hefty boom box to me!

We'll see what I can do about that crossover/limiter, but to be honest first of all I'm into delivering a solid base for crossover building and LS development experience. And as I mentioned, there are quite a few things on my plate as of now, you can always fortify that feature request by adding a feature request at gitlab.

Of course designing a boom box like this I can definitively see the benefits of having a fast acting compressor for pushing the SPL. That said, in your case I would even ditch the compression ideas and look more towards a really fast acting limiter. Maybe even look-ahead, introducing a minor delay, which can be compensated for.

Tfive 16th August 2019 08:54 PM

Another thing I have to say about this topic: I worked a little while as a sound engineer in live sound. All the amps there have fast acting limiters, especially in the base. To be honest, if you drive your amps into mild "clipping" you won't even hear it at the levels that are used in PA. What's different is: Engineers always get some kind of feedback how much a limiter is limiting or a compressor is compressing. Another drawback of LADSPA plugins, they don't provide any meaningful UI, not even a compression ratio in dB, which is IMHO a must for a compressor. So in the long term if really incorporating any sort of level shaping plugins there's IMO a must for monitoring the action of the plugins.

FYI as I also feature the possibility to boost/cut gain in every filter there's a high priority TODO to offer VU meters for all outputs. That way you can at least adjust your gain structure to fit your filters and not throw away any digital resolution. This is tied to the measurement_support branch though, as it uses pulseaudio live inputs and it's associated prerequisites.


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