Deconstructing the home theater pre-processor

Nyal Mellor

Industry Expert
Jul 14, 2010
590
2
0
SF Bay Area, CA, USA
#1
I wrote a blog article today about pre-processors and how their functionality might be deconstructed and split out to improve quality and ease ongoing upgrades. Thought you might be interested:

"Ahhh....the home theater pre-pro....my thoughts on them are basically summarized by the phase "can't live with them, can't live without them"! Modern pre-pros are the brain of all modern home theaters. An AVR (audio video receiver) is essentially a pre-pro and multi-channel power amplifier in one box. Pre-pro's do a number of essential things without which it would be virtually impossible to watch movies in surround sound. What if there was a better way to go about including the functionality of a pre-pro in your system? Could it be done in such as way that would make it modular and upgradeable when new improvements in video processing and room correction make their way to market? Many people say a pre-pro is like a mini audio and video computer. If so could we use a home theater PC as a pre-pro?"
You can read the rest here. Thoughts & comments?
 

edorr

WBF Founding Member
May 11, 2010
3,146
5
36
Smyrna, GA
#2
I wrote a blog article today about pre-processors and how their functionality might be deconstructed and split out to improve quality and ease ongoing upgrades. Thought you might be interested:



You can read the rest here. Thoughts & comments?
I never liked the notion of a pre/pro. Too much functionality stuffed in a single box, doing a half ass job at everything (or a 75% ass job for $30K). Then there is HDMI..... A very powerfull processor (like the HTPC you will be building) doing all the processing and an array of DACs or a single MCH DAC behind it is far more elegant.
 

Ron Party

WBF Founding Member
Apr 30, 2010
2,457
3
0
Oakland, CA
#3
Hi Nyal. Long time, no talk.

In your blog, you write a list of the main, secondary and tertiary purposes of a pre-pro. Included in the list of the main purposes is upmixing, for example, from 5.1 to 7.1. Included in the list of secondary purposes is hi-res audio format decoding.

I don't know if upmixing alone or in conjunction with audio format decoding covers it but I personally consider the main purpose for using a pre-pro, or at least one of the top 2 or 3 purposes, is for its surround processing. If I'm using a surround processor I'm doing so for its surround processing. I'm not writing about room correction. I'm not writing about eq or bass management. I'm writing about the kinds of things that L7 did and its successor, QLS, reportedly does, the latter of which was supposed to be released with the now shelved MP-20 to which Amir made excellent reference here at WBF in this thread.
 
Feb 11, 2012
1,286
1
0
Hangzhou, China
#4
I agree with the basic premise - that of deconstructing the unwieldy boxes of today's HT equipment, just I don't see using a HTPC as any kind of long-term solution. The PC as a consumer product is rapidly dying a death, its a bubble which is in the process of bursting. I'd like to see a more sustainable answer to this question and indeed I intend to work on it (in design terms) in the future.
 
Mar 21, 2011
193
0
16
Wisconsin
#5
Very interesting idea. I think something like this has the possibility of really becoming popular with today's tech savvy enthusiast as long as it can be streamlined to be user friendly and fairly easy to setup. I look forward to your future articles.
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,516
468
360
Manila, Philippines
#6
I think the future of HT will be wireless loudspeakers. Any pre-pro/AVR or HTPC should be able to support this somehow.
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,516
468
360
Manila, Philippines
#8
I don't think battery tech is anywhere near ready given the cost so I figure AC powered with streamed signal. I think it is a viable emerging market segment for HT because of the housing figures. Lots of renters compared to fully owned houses. Usually means you don't get to punch holes in walls and tear up rugs to hide rear speaker wires. Imagine if you could have your LCR wired but have the freedom to place your rears practically anywhere you want? I think that would be great!

Then if you move house or even cities, everything just goes in the U-haul trailer. Sweet!
 
Feb 11, 2012
1,286
1
0
Hangzhou, China
#9
Yeah I can see the arguments for that, have been over them in my mind dozens of times. I always end up figuring if you're going to run a mains cable you can run fairly thin power and signal (digital or analog) and have an active which is low voltage powered so doesn't need to meet code for the cable. If you're in a rented place are you going to install new AC mains right close to your rears? Besides which wireless tends to have dropouts, even with the best will in the world.
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,516
468
360
Manila, Philippines
#10
True. Rated extension cords are cheap though. Haven't seen too many rooms built with utility outlets on just one side of the room. We're not exactly talking about the highest fidelity here, but for sound effects or BGM, most I believe are a bit more forgiving. Flip a switch and move the speakers, instant second zone. Another cool possibility. The SONOS system uses Wi-Fi for command but it's own radio frequencies for signal I believe. Pretty robust in our house despite a lot of poured concrete. I haven't even noticed any mean dropouts. I can't say the same for Airplay. I used a bunch of Apple Expresses in the past. So maybe something like that, a dedicated spectrum.
 

FrantzM

Member Sponsor & WBF Founding Member
Apr 20, 2010
6,464
5
255
#12
Hi

I am quoting your blog premises here for the sake of clarity:

The functions of a pre-pro
Core. These are the pieces of functionality that any pre-pro must have in order to do it's job. We're assuming that the source signal is digital from a DVD or Blu-Ray.

Source selection
Volume control
Multi-channel digital to analog conversion
Delays and volumes for individual speakers
Upmixing, from 5.1 to 7.1 for example
Bass management


Secondary. There are a couple of items here which are 'nice to have' but are not necessary for a pre-pro to function.

High resolution audio format decoding (all blu ray players can decode these formats)
Room correction
Video scaling
Aren't we substituting a complicated box with another equally complicated and likely comolex to put together and set-up. What would be the price of such? Would the results be worth the cost?

Using for example a High End Sound Card would get you in the thousand easy. Now Processor, Power Supply, Enclosure, cooling and soundproofing could well get you in the vicinity of $2000, likely more.
I suppose a High End video card is part of the deal we can put aside video-scaling but we need to do well in video and gaming could well be close to $1000. Multiple inputs output may require multiple video cards ...
Then you need software, I am not sure of the cost but you are likely in the half thousand
Then you need to optimize this whole thing. What about things like Reliability? Ease of use? Support?

This gets you around $5000 easy IME. Aren't we in the province of substantial, good honest performance pre/Pro like the Denon 4311, Integra 80.3, etc? It becomes more flexible .. true to a point too much control leads to endless tinkering.
 

JackD201

[WBF Founding Member]
Apr 21, 2010
11,516
468
360
Manila, Philippines
#13
The point about not having to meet code wasn't so much the price, more the thickness and robustness of the insulation. It translates to less flexible, less easily concealed cable.
Now you're just being a wet blanket. :p You expecting class A operation and 6 figure micro-farad capacitance storage in a wireless speaker opus? Furniture would be doing the brunt of the concealing.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
590
2
0
SF Bay Area, CA, USA
#14
Hi Nyal. Long time, no talk.

In your blog, you write a list of the main, secondary and tertiary purposes of a pre-pro. Included in the list of the main purposes is upmixing, for example, from 5.1 to 7.1. Included in the list of secondary purposes is hi-res audio format decoding.

I don't know if upmixing alone or in conjunction with audio format decoding covers it but I personally consider the main purpose for using a pre-pro, or at least one of the top 2 or 3 purposes, is for its surround processing. If I'm using a surround processor I'm doing so for its surround processing. I'm not writing about room correction. I'm not writing about eq or bass management. I'm writing about the kinds of things that L7 did and its successor, QLS, reportedly does, the latter of which was supposed to be released with the now shelved MP-20 to which Amir made excellent reference here at WBF in this thread.
Hi Ron

How's it going!

The decoding of high resolution audio formats (DTS True HD and Dolby Master Audio) is something all blu ray players can do. Indeed if memory serves me correctly in the beginning most pre-pros couldn't decode a HD 'bitstream' into LPCM, and so this was done in the blu ray player which sent LPCM to the pre-pro.

By upmixing I mean expansion from 5.1 to 7.1 or from 2.0 to 5.1 or beyond using things like Dolby Pro Logic.
 

WLVCA

Member Sponsor
Nov 2, 2012
2,387
774
225
Tucson
#15
I don't have a dedicated theater room and I'm not so focused on SOTA performance for movies.

Bought an Onkyo TX-NR818 ($650.00) and I'm using it as a pre-pro. Driving the speakers with an Emotiva XPA-5.

Given the rapidly changing technology, I wasn't going to spend big bucks on a processor. I'll replace it in 4- 5 years with something else.

The 818 does have features I don't use.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
590
2
0
SF Bay Area, CA, USA
#16
Hi

I am quoting your blog premises here for the sake of clarity:



Aren't we substituting a complicated box with another equally complicated and likely comolex to put together and set-up. What would be the price of such? Would the results be worth the cost?

Using for example a High End Sound Card would get you in the thousand easy. Now Processor, Power Supply, Enclosure, cooling and soundproofing could well get you in the vicinity of $2000, likely more.
I suppose a High End video card is part of the deal we can put aside video-scaling but we need to do well in video and gaming could well be close to $1000. Multiple inputs output may require multiple video cards ...
Then you need software, I am not sure of the cost but you are likely in the half thousand
Then you need to optimize this whole thing. What about things like Reliability? Ease of use? Support?

This gets you around $5000 easy IME. Aren't we in the province of substantial, good honest performance pre/Pro like the Denon 4311, Integra 80.3, etc? It becomes more flexible .. true to a point too much control leads to endless tinkering.
Yes, that is probably true. This whole project is a proof of concept. I don't even know if it will work reliably and consistently at this stage! Initial parts costs excluding the multi-channel DACs are around $1.5k.

The biggest advantage I see with the approach is that the pre-pro has been broken down into individual components which can be hopefully more easily and cheaply upgraded over time as video and room correction advances come down the road. One can even swap out DACs for the latest 'flavor of the month'. I hope that the audio performance will be a step above the Integras and Denons of the world and more like the DataSats.

I imagine a better approach than using off the shelf software (Windows in particular) would be to use a mostly locked down custom developed Linux o/s with 'plug-in' applications for individual tasks such as audio DSP, video DSP, etc.
 
#17
Nyall, I applaud the effort and will follow along closely.

I do have an HTPC, but mainly use it as an audio server and playback source to my Denon AVP pre/pro.

The one thing I believe you missed in your excellent summary is that a major role for the Pre-pro is to coordinate the highly interrelated aspects of audio signal timing (for reduced jitter and time alignment) and volume interaction (e.g. Audyssey Dynamic EQ). When a pre decodes codecs like trueHD, the resulting PCM streams are clocked using the the pre's master clock, the output D/A is also clocked to that, as are all other digital signal processing circuits in the box. This ensures an extremely low level of jitter. By knowing what the current source level and the users selected volume setting, it can apply certain dynamic EQ or volume management algorithms to increase casual usability.

I do agree that today's pre is overloaded with too many features and should leave out the video processor and many non-core features.
One area I've been torn on is built-in DLNA playback, from a purely audio quality, that's the best way to get streamed ripped music into the box and benefit form the tight clocking of internal components. However, the typical pre-pro DLNA services suck. My AVP can barely handle 24/96 FLAC in 2ch, can't handle multichannel.

What's needed is for HDMI to support one of the many audio clocking options as a standard and then we can have a greater selection of sources that will still deliver a quality experience.
 
Last edited:

Nyal Mellor

Industry Expert
Jul 14, 2010
590
2
0
SF Bay Area, CA, USA
#18
Nyall, I applaud the effort and will follow along closely.

I do have an HTPC, but mainly use it as an audio server and playback source to my Denon AVP pre/pro.

The one thing I believe you missed in your excellent summary a that a major role for the Pre-pro is to coordinate the highly interrelated aspects of audio signal timing (for reduced jitter and time alignment) and volume interaction (e.g. Audyssey Dynamic EQ). When a pre decodes codes like trueHD, the resulting PCM streams are clocked using the the pre's master clock, the output D/A is also clocked to that, as are all other digital signal processing circuits in the box. This ensures an extremely low level of jitter. By knowing what the current source level and the users selected volume setting, it can apply certain dynamic EQ or volume management algorithms to increase casual usability.

I do agree that today's pre is overloaded with too many features and should leave out the video processor and many non-core features.
One area I've been torn on is built-in DLNA playback, from a purely audio quality, that's the best way to get streamed ripped music into the box and benefit form the tight clocking of internal components. However, the typical pre-pro DLNA services suck. My AVP can barely handle 24/96 FLAC in 2ch, can't handle multichannel.

What's needed is for HDMI to support one of the many audio clocking options as a standard and then we can have a greater selection of sources that will still deliver a quality experience.
Hi Jonathan, is the clocking the reason why people recommend decoding in the pre-pro rather than in the blu-ray? I guess if we used a multi-channel external USB / FW DAC operating in async mode or a card like the Lynx AES16 with a word clock input then we would be ok from a clocking perspective?
 

mojave

New Member
Oct 29, 2010
251
0
0
Elkhorn, NE
#19
I enjoyed reading the article. Did you wait specifically until 12:34 to post it? :D

For a little historical perspective, you might want to browse the "Please post your "HTPC as preamp/processor success stories"" thread at AVS from almost 10 years ago (March 2003). At that time the emphasis was more on the audio card's drivers and HDTV Tuner software than on playback software. There was also an interesting "High-End Analogue Soundcard Shootout" thread at the same time that compared RME, Lynx, and M-Audio soundcards to a dCS DAC and Lexicon Pre/Pro.

Here are a few highlights my own HTPC as Pre/Pro timeline just for fun:
  • 2003: Build first HTPC and used M-Audio Revolution 7.1 soundcard for decoding, upmixing, and bass management
  • 2004: Purchased Theatertek 2.0 software with advanced audio pack - used for all movie playback, decoding, and bass management
  • 2005: Starting using JRiver Media Center V9 for music only
  • 2005: Purchased MyHD MDP-130 HDTV Tuner for HTPC
  • 2007: Switched to JRiver Media Center for movies, too
  • 2007: Sent digital out from HTPC to BehringerDCX2496 for bass management
  • 2009: Started experienting with VST plugins in JRiver for Parametric Equalization
  • 2009: Started using JRiver's Bass Management
  • 2010: Requested madVR be added to JRiver
  • 2010: Used JRiver for parametric EQ for music/movies
  • 2012: Able to route all computer audio through JRiver for PEQ/Bass Management
  • 2012: Purchased Audiolense for advanced room correction
  • 2013: Active Crossovers with Audiolense?
 

Nyal Mellor

Industry Expert
Jul 14, 2010
590
2
0
SF Bay Area, CA, USA
#20
I enjoyed reading the article. Did you wait specifically until 12:34 to post it? :D

For a little historical perspective, you might want to browse the "Please post your "HTPC as preamp/processor success stories"" thread at AVS from almost 10 years ago (March 2003). At that time the emphasis was more on the audio card's drivers and HDTV Tuner software than on playback software. There was also an interesting "High-End Analogue Soundcard Shootout" thread at the same time that compared RME, Lynx, and M-Audio soundcards to a dCS DAC and Lexicon Pre/Pro.

Here are a few highlights my own HTPC as Pre/Pro timeline just for fun:
  • 2003: Build first HTPC and used M-Audio Revolution 7.1 soundcard for decoding, upmixing, and bass management
  • 2004: Purchased Theatertek 2.0 software with advanced audio pack - used for all movie playback, decoding, and bass management
  • 2005: Starting using JRiver Media Center V9 for music only
  • 2005: Purchased MyHD MDP-130 HDTV Tuner for HTPC
  • 2007: Switched to JRiver Media Center for movies, too
  • 2007: Sent digital out from HTPC to BehringerDCX2496 for bass management
  • 2009: Started experienting with VST plugins in JRiver for Parametric Equalization
  • 2009: Started using JRiver's Bass Management
  • 2010: Requested madVR be added to JRiver
  • 2010: Used JRiver for parametric EQ for music/movies
  • 2012: Able to route all computer audio through JRiver for PEQ/Bass Management
  • 2012: Purchased Audiolense for advanced room correction
  • 2013: Active Crossovers with Audiolense?
Thanks for the link! I kind of knew that a while ago people had looked seriously into using the HTPC as a pre/pro but then it fell out of favor. Hence why I called the last section 'HTPC Redux'.

10 years ago I was living in London, I think I might have had a pair of PMC monitors and some Naim amps...I forget, it was a long time ago. Music appreciation at that time for me was about going to bars to watch bands or clubs. 2003 in London was epic for dance music. I lived right opposite a major nightclub and went there a lot. I didn't even know home theater existed!
 

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