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Linux PC DSP & Crossover

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  • Linux PC DSP & Crossover

    I thought I'd post up my latest project, as there was some interest in another thread; A Linux PC music player with processor based DSP functionality and a 4-way crossover. I'm no Linux expert. In fact, I spent a good part of the last week (vacation time) climbing the Linux learning curve to get it to work. My description below is pretty bonehead, with just the basic stuff. I had to Google every step, so I'm not qualified to get into too much technical detail. Heck, I'm surprised I was able to get anything to work.

    Nothing fancy. I used a slightly dated MSI E350IA-E45 mITX motherboard with an integrated processor, video, and sound. This board is NLA - there's better for the price now , but I already had it laying around. The key is 8 channels of onboard audio out. Also, I used 4G ram, a 120GB SSD for the operating system and 1TB HDD for media. That's it. No other add-ons other than wifi and peripherals.

    I used Linux Mint, along with Google Play, Clementine Music Player, and Google Chrome for source material.

    The foundation to the audio processing is "Jack"

    This allows the user to intercept audio from each hardware or software source, route it through any number of audio plug ins, and ultimately assign the output to to hardware audio out. Part of the process is configuring Linux to allow real-time audio processing, and prioritizing audio over other processes. I wasn't worried about low latency, since I'm just using the system for playback - OK since I'm using a pretty low power computer.

    Also needed was GStreamer. This will grab audio from applications for use as a "Jack" input.

    And finally I used "Calf Studio" plugins for audio processing. There's a whole world of plugins that I haven't even begun to explore, but Calf has a package that includes all the stuff I'll use, including multi-channel parametric equalizers, multi-channel crossovers and compressors. They also have stuff that's just fun to play with, like bass enhancers and a Leslie Speaker simulator.

    You can keep stacking the plugins, and use "jack" to route audio through them as you like.

    How does it perform?
    With my low power system, I honestly didn't expect it to work at all. To the contrary, I've been able to route audio through multiple plug-ins with no issues. It just works like a bunch of real pro-audo hardware.

    I haven't had a chance to route outside sources, like a turntable, into the system. Calf has an RIAA plugin, so it remains to be seen how well I can get that to work.

    This may not be the "ultimate" in audiophile, using compressed music and cheap onboard sound, but I'm pretty stoked. There's a lot more potential here with a bit more learn'n and better hardware.

  • #2
    Re: Linux PC DSP & Crossover

    Sounds like something fun to play with. I Googled the MB you're using and tracked down with processor which appears to be a very modest AMD APU. I found this performance review from when it came out in 2010. It's pretty amazing that you can do all this with so little muscle.

    C-Note Iron Driver Build
    The Cherry π's


    • #3
      Re: Linux PC DSP & Crossover

      Nicely done. I am afraid that one of these days I may have to make just such a plunge should my 10 year old DEQX give up the ghost. And doing it with an unfamiliar OS, wow. And that you did it with so little horsepower may have much to do with the choice. Way to go!


      • #4
        Re: Linux PC DSP & Crossover

        Thanks for the update.
        So you route the separate bands of LR4 crossover out to one of the 5.1 audio jacks?

        You did incredible work to get Jack all set up. I've set it up several times over the years - the problem I had
        was that when I did a system update it would tend to break Jack - but for a dedicated audio PC it should not
        be a big problem.

        I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
        "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

        High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
        SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
        My Voxel min sub Yet-another-Voxel-build

        Tangband W6-sub


        • #5
          Re: Linux PC DSP & Crossover

          This looks like a really neat project for during the cold winter months up here, awesome. Thanks for sharing the sketch of the process!
          Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
          Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club


          • #6
            Re: Linux PC DSP & Crossover

            Originally posted by donradick View Post
            Thanks for the update.
            So you route the separate bands of LR4 crossover out to one of the 5.1 audio jacks?
            It's outputting 4 stereo channels from the card, green is the sub, black is the woofers, orange the mids, and grey the tweeters.

            I'll probably play around with applying a limiter, or some compression, just on the sub channel. This is the front end to "party speakers", and I tend to over drive the sub after a few drinks. :o

            I might also try outputting to separate usb sound to get rid of some noise issues (see my other thread), but that's for another day..


            • #7
              Re: Linux PC DSP & Crossover

              I think a single install of UbuntuStudio 14.10 includes everything except Clementine. Nice discovery of a free crossover.


              • #8
                Re: Linux PC DSP & Crossover

                This looks very interesting. Now I need a multichannel card...
                My Statement monitors
                My Piccolatas
                My LM3886 amp


                • #9
                  Re: Linux PC DSP & Crossover

                  Originally posted by SHYNOLA View Post
                  I think a single install of UbuntuStudio 14.10 includes everything except Clementine. Nice discovery of a free crossover.
                  Cool, I didn't know this existed. It probably would have saved me some time researching and setting everything up. I guess the upside is that I learned a little doing it the hard way.

                  I'll have to look into Gladish - It looks like it might be a little more friendly than Jackctl.

                  Now I'm motivated to build another Linux/DSP box. I don't really need another one, but I'm sure I'll generate a "need". I don't really like the Umbuntu Unity interface, but that could be changed easy enough.

                  Thanks for the tip.


                  • #10
                    Re: Linux PC DSP & Crossover

                    Pretty neat. I'll have to look into this at some point. It'd be neat if there were a solution for Windows that was as robust and low cost. Maybe some day.


                    • #11
                      Re: Linux PC DSP & Crossover

                      I wish to do the same thing (ubuntu 14.04) for a 5.1 system with the main speakers biamped. If I can demonstrate (do all the programming) that I can realize the low pass (subwoofer), high pass (center and rear spekers) and band pass plus equalization (main speakers) using linux software I would order the parts express cbt36k speakers for my new main speakers. I have a Xonar D2 sound card (7.1 channels) to drive the power amps.

                      My main question for you is that my media server is kodi which does not allow you to redirect the audio output. You have to select a sound card for audio output from within kodi. Does your setup allow for a vitual sound card so I can capture the kodi output for processing and then send it to the physical sound card? Note that any delay introduced by the processing is not a problem with kodi since kodi allows your to either advance or delay the video signal with respect to the audio. kodi also has recently undergone a complete rewrite of the audio engine to improve sound quality. Using kodi and kodi plugins with MythTV backend and MakeMKV I can now use kodi to -

                      Watch and record live TV (Ceton Infinitv 6 cable card tuner)
                      Play audio and video files
                      Watch amazon prime and 1channel
                      Play commercial CD, DVD, and Blu Ray disks

                      The only thing I cannot do with kodi is play my legacy analogue sources (turntable with preamp and open reel tape deck). Any comment and suggestions from you would be greatly appreciated