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HTPC DSP versus dedicated DSP platforms for loudspeakers
HTPC DSP versus dedicated DSP platforms for loudspeakers
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Old 3rd July 2015, 06:37 PM   #1
diyaudnut is offline diyaudnut  United States
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Default HTPC DSP versus dedicated DSP platforms for loudspeakers


I wanted to start this thread to capture thoughts and discussions from experts in this field and those who have experience in developing and using these setups.

Some of us primarily enjoy digital music sources
1. High resolutions audio tracks
2. CD music
3. mp3/online streaming

This fed to a full active DSP XO/DRC, followed by multi-channel amplification to drive multi-way stereo loudspeakers can be a common setup. It is something I am currently working on putting together.

I find there are two options for DSP.
#1. Dedicated DSP platforms such as
a. MiniDSP
b. Hypex DLCP
c. WAF Najda
d. http://www.diyaudio.com/forums/digit...c-project.html
e. FreeDSP

#2. A high performance HTPC running software DSP, followed by USB audio interface or dedicated multichannel soundcard

One such example of an HTPC is Assassin Audiophile HTPC. This one looks overpriced and a comparable HTPC can be put together for a lot cheaper.
But some salient points to note are
1. 3.4 GHz i7 4770k Intel Haswell Processor (4 core, 8 threads, TDP around 45W)
2. 8-16GB RAM
3. SSD storage + HDD for music storage
4. Fanless passive cooling
5. CD/Blueray drive
6. USB/Firewire ports
7. network connectivity
8. Windows platform (Linux, mac a possibility, though my personal preference is Windows)

The HTPC primarily acts as digital music server, software DSP XO + other filters, SW music player (JRiver, foobar etc).
The HTPC can interface to a DAC through USB or firewire port. Multiple options here:
1. U-DAC8 | miniDSP
2. Pro Audio Interfaces such a Motu: MOTU.com - Overview, MOTU.com - Tech Specs
3. Something put together using Amanero OR XMOS + Buffalo DAC

One thing that’s not clear is the use for all the additional features provided by a pro interface in this application. An alternative is to use a dedicated MC soundcard in the HTPC for DAC duty,
http://www.lynxstudio.com/product_detail.asp?i=16 (expensive)

Another intriguing product with loads of DSP power appears to be http://www.uaudio.com/uad-plug-ins/uad-2-satellite.html , with no clear way to apply for loudspeaker management.

1. Can the i7 outperform dedicated DSP chips for FIR/IIR filters for this application. Note there is overhead for the OS, music player etc.
2. Please comment on relative pros/cons of HTPC vs dedicated DSP
3. Please list useful software for filter design, DSP, music player etc for the HTPC setup
4. Compare pro audio interface against high quality MC soundcard for the HTPC
5. What are other good options for MC sound cards
6. Quality of clocks, digital and analog implementation matter so the products will differ on this and hence the price point

Last edited by diyaudnut; 3rd July 2015 at 06:42 PM.
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Old 3rd July 2015, 11:56 PM   #2
LewinskiH01 is offline LewinskiH01  Argentina
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Location: Buenos Aires
Hi. I'm going down this road, but it seems to be less travelled than I thought it would. I used to have a Rotel RCD1082 CD player, but eventually sold it after I realized I was only listening to my audio laptop since the sound quality was better and more convenient. Eventually built a purpose-designed audio PC and sound quality improved a lot more. I have now added Acourate software for digital room correction and I'm making my way towards a fully active 4-way system where Acourate is also used for digital crossovers, driver linearization and time-alignment.

My audio computer was built in Feb-14. It's meant to play audio only - no video. Mobo is Intel S1200KPR, which is a server mobo. I would turn off wi-fi, bluetooth, etc anyway, so might as well not spend on those. Wi-fi is supplied through LAN and a wi-fi bridge, BTW. Processor is Intel Xeon E3 1265lv2, 8GB RAM, 64GB SSD for OS/JRiver/Acourate, SSD for music files, Paul Pang Audio USB v2 card, Streacom FC8 fanless case. Pretty much in line with your list, although I wanted to avoid any type of motor inside the PC (for their EMI/RFI) so opted not to have an internal drive. I have a linear power supply too.

Operating system is Windows Server 2012 R2 running in core mode. Core mode makes a big difference. Also running AudioPhil's Audio Optimizer, which makes a huge difference. Player is JRiver. It's a headless server (no screen), and I control JRiver through JRemote either from an iPad or my Android phone. Works wonders. And I'm also running Acourate for DRC (for the time being) and I'm very happy.

For reference, my system is Audiophilleo USB-to-SPDIF converter with PurePower, into a Metrum Octave DAC, into a Lamm LL2 preamp, into a pair of DIY Rythmik subs (to their internal crossovers) and the output (above 80Hz) is fed into a McIntosh MC275 amp, then feeding a pair of B&W 804S.

So much for what I already do. Here's what I plan on doing: I bought a Lynx Hilo multichannel DAC and I'm building a pair of Hypex UcD400HG monoblocks. The plan is to use Acourate to create digital crossovers and feed 6 channels to the Hilo, and have the Hilo directly drive the subwoofers, the UcD amps (driving the 804S woofers, and the MC275 driving the 804S midrange/tweeter. I plan to use Acourate to linearize the drivers, time-align them, and of course for DRC.

This will be a huge leap for me. It took a lot of researching to even allow the idea of a DAC driving amps directly would overperform my beloved Lamm pre. I guess I will be able to answer this when I try it.

Many multichannel cards available. Lynx Aurora has like 16 channels, although they are lower sound quality than the Hilo. Prism Sound Titan was my top choice, but decided to go with Hilo now.

Check these for two very good primers on Acourate potential:
Computer Audiophile - Acourate Digital Room and Loudspeaker Correction Software Walkthrough
Computer Audiophile - Advanced Acourate Digital XO Time Alignment Driver Linearization Walkthrough

I hope this helps!

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Old 4th July 2015, 12:58 AM   #3
CharlieLaub is offline CharlieLaub  United States
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Join Date: Mar 2007
Location: Michigan
Originally Posted by jojip View Post
#2. A high performance HTPC running software DSP, followed by USB audio interface or dedicated multichannel soundcard
I'm currently going down this road. I have written and tested (but not yet released) some LADSPA plugins that can be very easily used under linux to process audio in real time into N filtered channels, e.g. to implement an N-way crossover. My plugins implement filters using an IIR digital scheme, which keeps the CPU demand to a minimum. If you want to consider that route, you likely do not need to throw so much money at the computer hardware.

For example, in order to build and test my plugins I recently put together a bare-bones system (motherboard, RAM, HD) for about $175 in parts. The motherboard has onboard 7.1 channel audio, can be powered by a DC supply (laptop brick type) providing as little as 24Watts (I verified this), and has passive CPU cooling for four cores. This makes the system very quiet (it would be totally silent if I used an SSD, but its nearly so already). I tested the audio I/O, supplying audio via the line input and taking audio back out via the "front speaker" outputs on the rear panel to my test gear. Frequency response, S/N and distortion are about as good as an early model CD player, but not mind blowing. Keep in mind that these measurements were made by going from the digital domain in my test gear computer to analog, then back to digital at the mobo line input, then through the filter, then back to analog, and finally back to digital at the input of my test gear. For $175 I was not expecting something that was top of the line, but it's certainly more than adequate for loudspeaker crossover work. Even with all the A-D and DA conversions the measured performance compares favorably to some hardware-based DSP crossovers, but comes with the versatility of a full-blown computer with an OS. See attached images for my measurements - NOTE, these were made using a 96kHz sampling rate while processing the signal internally using a single IIR filter that only modified the amplitude by -1dB.

If you are looking for better audio specs you might check out some of the 7.1ch cards that are available. Some of these are not expensive (e.g. <$100) yet have very impressive performance (on paper at least).
Attached Images
File Type: png Baytrail-1 FR measurement.PNG (33.9 KB, 501 views)
File Type: png Baytrail-1 quick distortion measurement.PNG (44.6 KB, 502 views)
File Type: png Baytrail-1 STEPS distortion measurement.PNG (46.3 KB, 501 views)
Visit my Audio Web Page <<--CLICK TO LEARN MORE-->> Get my LADSPA plugins

Last edited by CharlieLaub; 4th July 2015 at 01:04 AM.
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Old 4th July 2015, 05:41 PM   #4
diyaudnut is offline diyaudnut  United States
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Thanks Guys
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Old 6th July 2015, 02:57 AM   #5
diyaudnut is offline diyaudnut  United States
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Charlie, I have been following the development on your thread. very impressive.
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Old 6th July 2015, 05:07 AM   #6
Sangram is offline Sangram  India
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HTPC DSP versus dedicated DSP platforms for loudspeakers
In use a DSP for XO and loudspeaker management. An old e-MU card, but it has onboard hardware DSP so it's a little further away from what you're looking for. It has limitations, resampling all signals to match the internal DSP clock, and some limitations on filter slope shapes/types.

However since I'm only using it for a sub/sat XO, it works out quite well. I also do iron out some of the quiirks of the in-room response, and that would be a custom application. In my experience of tdedicated DSP ala Behringer DCX/dBx, those platforms are a lot more flexible but there are limitatioins on DSP power. That is inevitable no matter what solution you pick.

I'm not personally inclined to use CPU for DSP, at least not one that also has to serve the main audio playback stream and definitely not if it's running Windows, which is not very CPU-efficient. Probably just a hangover from the 90s. But I prefer using cheaper CPUs and a hardware solution when its needed. The current technology cycle means that you have to reconfigure too much and buy too much new stuff if one part in your system goes south.

That said, most modern i5 or better CPUs should be able to tackle a two-way crossover with ease. Once it starts getting more complex than that, well, I'm not so sure.
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Old 6th July 2015, 06:14 AM   #7
diyaudnut is offline diyaudnut  United States
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I am not quite sure if 4 modern 64-bit cores running over 3GHz and with lots of internal and external memory bandwidth are unable to process DSP algorithms at par with DSP processors at significantly lower frequencies albeit with DSP accelerators.

DSP processors are still instruction fetch/execute CPUs but with optimized architecture for DSP workloads and with some HW assist accelerators.

I do agree that a massive OS load and a complex music player would likely bog the CPU down.

Anyone with direct experience with objective and quantitative comparison of DSP performance should kindly comment.
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Old 6th July 2015, 06:19 AM   #8
diyaudnut is offline diyaudnut  United States
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How about the HTPC performing some room correction, phase/amplitude EQ using filters generated by rephase, charlie's application above, Acourate etc, while a dedicated DSP board like Najda performs IIR loudspeaker XO.

Is such a loop for partitioning the DSP workload practical?
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Old 6th July 2015, 06:51 AM   #9
Sangram is offline Sangram  India
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HTPC DSP versus dedicated DSP platforms for loudspeakers
It is possible to partition DSP tasks between two - or more - different boxes. Large studio environments usually do this already for production.

Every DSP task has a CPU cost whether it is in a computer or inside a DSP unit (see this: UAD Instance Chart), the more complex and accurate the effect, the higher the CPU cost. Whether your CPU is up to it depends on the CPU and taskl you assign it and without knowing both of those exactly, you cannot determine if it will be enough or not.

Speed of the CPU is not everything, neither is the bus width. A modern, general-purpose PC is processing thousands of instructions every second that have nothing to do with your audio stream, and it is near-impossible for the end-user to prioritize threads or get them to run in real-time.

The closest thing to learn from is actually music production, which uses a mix of real-time plugins, effect boxes, outboard DSP and mixed-down tracks with software filters applied (because some filters are simply too CPU-intensive for real-time playback). There's something to learn from that side of the game.
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Old 6th July 2015, 06:57 AM   #10
diyaudnut is offline diyaudnut  United States
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Apollo 8 Thunderbolt 2 Audio Interface

Someone with the right expertise should look into the possibility of using this platform for complete DSP loudspeaker management. With 4 SHARC processors there is plenty of DSP power to harness.

Appears to be a closed platform though, so likely to be just a pipedream.
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