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LADSPA plugin programming for Linux audio crossovers
LADSPA plugin programming for Linux audio crossovers
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Old 25th May 2015, 04:15 PM   #21
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by Dr Jim View Post
Charlie -

Watching your work with great interest - have used the Pi boards as S/PDIF music sources for some time now, with the HiFiBerry Digi and Digi+ adapters from Switzerland:
https://www.hifiberry.com/digiplus/
which have worked surprisingly well as headless music streamers feeding a MiniDSP NanoDIGI which provides the 2.1 crossover for our primary system
I'm planning doing something similar, except with miniDIGI+2x4 boards. I think it's a great application for the Pi.

Quote:
Originally Posted by Dr Jim View Post
I was quite stoked to see the Pi quad-core boards released at an affordable price, grabbed one from Newark's first batch, and have had very good results from it ever since.

I've an argument with using HDMI output that isn't functional (HDMI on the Pi does appear to be less glitchy than either its USB or PWM/analog outputs), but is more a conceptual irritation - it just bites me to spend a fair amount of time & effort to massage a digital data stream to have exactly the shape and content that suits me, only to feed it to a consumer-grade DAC in a HDMI=> Analog Box of Unknown Origin.

Yeah, this <could> work well, but there's just not the same richness of back-end choices as there are with more conventional DACs.
Well, you can't have everything and have it low cost! I'm looking into HDMI out --> HDMI audio extractor as a solution. You are correct in that there is essentially no information on the web about the performance of the extractors in terms of THD, noise floor, etc. But they are not all that expensive, so I will just try one and measure it. From what I can tell from reading up on the web, I should be able to get at least 6 channels at 48kHz out of this arrangement without any tweaks like recompiling the kernel, etc. I am used to working with 48kHz streams from the crossover standpoint, so this is not at all a limiting factor for me.
Quote:
Originally Posted by Dr Jim View Post
Heck, the blessed Pi is such an inherently cheap platform, that I wonder if a distributed system using a Pi/DAC combination at each speaker fed from 100Mb ethernet might not be both cost effective and very listenable.

Obviously, synchronization between the 2 ...N channels will be a non-trivial issue, but it looks like there are aleady several approaches to managing this problem:
I have used a single Pi (so far) to successfully set up a streaming audio system over my home LAN using multicast. This took a lot of fiddling until I got the stream to be glitch/dropout free. I'm hoping, since I am using multicast, that I can have multiple synchronized pi receivers, well at least one in each speaker to start with.
Quote:
Originally Posted by Dr Jim View Post
A rather brute-force low-level approach with the clock signalling inserted into the ethernet packet headers:
Synchronous Ethernet - Wikipedia, the free encyclopedia
And a bunch of protocols developed for the Pro Sound world here:
Audio over Ethernet - Wikipedia, the free encyclopedia
But [SIGH!] it looks like the bandwidth of AOE (Audio Over Ethernet) is shockingly high because of the topologies requirements for maximum redundancy and 'hardening' for use in commercial venues.
Still, it would be interesting to have multiple Raspberry Pi's sharing a common audio network (perhaps running the AES/EBU protocol layer on a cheap S/PDIF hardware layer?) - there's something very appealing in the idea of $100 computer+DAC+crossover device sitting behind powered speakers for all the channels of a home theater.
"But I digress" ... (I Leonardo - Ralph Steadman )

Cheers

Jim
I'll be posting results when I have them. For now I am just waiting for the new hardware to show up so that I can start experimenting.
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Old 26th May 2015, 04:35 PM   #22
CharlieLaub is offline CharlieLaub  United States
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The last filters that need to be added are delay related. I another thread I have been musing about how to implement fraction delay and it seems I have narrowed that down to the Thiran AP for fractional delay plus a delay line. Combined, these should provide all the delay functionality necessary and will be computationally "light weight". I will probably limit the Thiran AP to order 10 or less so that the coefficient precision can be handled by doubles. I don't really see why someone would need/want to use a higher order than 10 anyway.
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Old 6th June 2015, 08:51 PM   #23
CharlieLaub is offline CharlieLaub  United States
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UPDATE:
I'm currently bogged down trying to get my Raspberry Pi 2 to output multichannel audio. I've been playing around with it using Raspian and so far I'm not all that impressed and I have run into problem after problem. I am planning to install Ubuntu 15.04 MATE and give that a try. If all else fails I will move up to a mini-itx PC (have wanted to try that anyway) but the cost for the hardware just about quadruples with that platform so hopefully I can get the R-Pi 2 to work for me.

Once I get a stable multichannel audio platform working under Linux I will start to compile and test the plugins.

If you have some good Linux Fu and want to help me figure out some Pi-2 issues, drop me a line. It would be much appreciated.
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Old 7th June 2015, 11:36 AM   #24
Odal3 is offline Odal3  United States
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Using the raspberry pi was my hope as well, but I haven't tried it yet since I don't have a multichannel DAC or HDMI soluton yet. Is it the mpd/ecasound approach you are trying to get to work?
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Old 7th June 2015, 11:29 PM   #25
jmccanna is offline jmccanna
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Quote:
Originally Posted by CharlieLaub View Post
UPDATE:
I'm currently bogged down trying to get my Raspberry Pi 2 to output multichannel audio. I've been playing around with it using Raspian and so far I'm not all that impressed and I have run into problem after problem. I am planning to install Ubuntu 15.04 MATE and give that a try. If all else fails I will move up to a mini-itx PC (have wanted to try that anyway) but the cost for the hardware just about quadruples with that platform so hopefully I can get the R-Pi 2 to work for me.

Once I get a stable multichannel audio platform working under Linux I will start to compile and test the plugins.

If you have some good Linux Fu and want to help me figure out some Pi-2 issues, drop me a line. It would be much appreciated.
I believe that problem is that the Pi 2 USB shares throughput with the Ethernet. That means it has limited bandwidth for I/O. There is a way to turn off the Ethernet and maximize the available throughput. If I make progress or someone else knows how that may be enough. I have successfully gotten the PI 2 to play a multi-channel per Richard Taylor's instructions but only when the origin file is in the Pi already.

James
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Old 8th June 2015, 12:27 AM   #26
CharlieLaub is offline CharlieLaub  United States
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I finally got the Pi2 to produce some useful audio. I discovered that a miniDSP miniSTREAMER (USB --> SPDIF out) is recognized on boot up, almost like a PNP device. Shows up with aplay -l with a bunch of modes, including the SPDIF out and multichannel modes up to 7.1 audio. The miniSTREAMER also has an SPDIF input, so this could be a way to get SPDIF into the Pi if I want to do that in the future (I have some evil plans that might work with this). I am almost tempted to get a multichannel spdif or I2S input DAC to pair with it, but I think that is the wrong road (see below) for multichannel audio and crossover work.

Using the Pi2+miniSTREAMER I did some extensive listening trials today using VLC as both the send (from another PC) and receive (on the PI) client, multicasting a transcoded (48kHz AAC/MP4 @320kbps) stream. Works like a charm over my LAN with the PI2 connected via a WiPi USB dongle. So my current near term plans for the Pi are to use a pair of them to implement streaming audio for a pair of loudspeakers (with one PI in each). This will be added to the input of the existing system of: SPDIF input --> miniDIGI --> miniDSP 2x4 --> multichannel amplifiers. That's a lot of hardware!

For the multiway LADSPA crossover client, It seems now very likely that I will throw in the towel with the Raspberry Pi and go with the mini-ITX computer that I have been eyeing. It has onboard 7.1 audio via Realtek ALC892 Audio Codec with analog audio output jacks on the rear panel. The system should be able to handle both streaming audio and the crossover processing with the analog outputs connected directly to the amps. I have seen rightmark testing of the audio from the board and it looks better than many computer sound implementations, and perfectly acceptable for my needs. I think I can put together the system hardware for about $200 and will use the new Ubuntu distro.
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Old 8th June 2015, 03:42 AM   #27
Odal3 is offline Odal3  United States
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Did you see this Apr 12, 2015 comment on Taylor's page:

"A good alternative is to send the audio over hdmi. AFAIK there is no alsa driver that can output 6-ch audio directly to hdmi on the Pi, but you could pipe the audio from ecasound to omxplayer, which does do multi-channel audio (a feature I requested for this purpose)."
Digital Crossover/EQ with Open-Source Software: HOWTO | Richard's Stuff
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Old 8th June 2015, 05:28 AM   #28
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by Odal3 View Post
Did you see this Apr 12, 2015 comment on Taylor's page:

"A good alternative is to send the audio over hdmi. AFAIK there is no alsa driver that can output 6-ch audio directly to hdmi on the Pi, but you could pipe the audio from ecasound to omxplayer, which does do multi-channel audio (a feature I requested for this purpose)."
Digital Crossover/EQ with Open-Source Software: HOWTO | Richard's Stuff
I believe I tried using omxplayer to play a multichannel WAV file. It either didn't work, only output 2 channels, or the bit depth was not supported (e.g. 24 bit). I have not seen a report of 24 bit audio working on the pi without downsampling to 16 bits when output is through alsa. All-in-all it's too sketchy for me at this time. I did buy TWO hdmi extractors and I may use the Pi2 for this application in the future, but for now I will be pushing on with some other hardware that I believe will prove to be easier to work with in the short term while I use the Pi2s for streaming audio with SPDIF output.
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Old 13th June 2015, 01:13 AM   #29
CharlieLaub is offline CharlieLaub  United States
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UPDATE:

I purchased and put together a mini-ITX FF system and installed Ubuntu 15.04. After taking a couple of days to get used to the desktop and install and setup various components that were needed I attempted to make some headway on this project.

Today I enjoyed some success on several fronts:
  • I tested out the onboard sound - I'm able to play test files using speaker-test and/or audio via apps to all 8 output channels, or a subset thereof.
  • I figured out how to set up a persistent ALSA loopback device.
  • I tested out ecasound using a test file.
  • I tested out the loopback device by playing to it from an app, set up ecasound to accept that as input, and then had ecasound send that to the onboard sound analog outputs.
I will eventually add ecasound commands to process the audio stream using the LADSPA plugins.

Speaking of the LADSPA plugins, I couldn't get my plugin code to compile successfully, which was a little disappointing. I was able to get Richard's rt-plugins to compile and build into the actual plugin file, so I will have to go back and take a look at my code and re-write it to more closely follow Richard's, at least until I get a better grasp on exactly what is going on within the code.

I'm definitely more confident that I can get this to fly now that I have gotten these things more or less ironed out.
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Old 13th June 2015, 01:19 AM   #30
jplesset is offline jplesset  United States
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Great news! sounds like you're most of the way there.
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