Computer as a Preamp

B

bloosqr

Audiophyte
Hi guys .. I haven't posted here in ages but I am trying a little experiment on a DIY upscaling preamp / surround system that I wanted to pass by you guys to see if anyone here has done anything similar. I used to DJ/remix so I had a slew of pro studio gear lying around and having vague geek tendencies I am trying to setup a system that uses a computer as an upscaling / decoding player. If this doesn't work or ends up simply being too annoying I'll buy the onkyo-886 or the 5507 and go that route.

I *think* this approach has certain advantage over going the standard high end receiver/preamp route in this day and age (and certain disadvantages)

The equipment I am using for this experiment is

4 Mackie 824's as surrounds (Near Field Reference Studio Monitors .. basically flat response tweaked for nearfield of course, which you really can compensate for ideally)

1 Mackie 626 as a center channel (I just paid an absurd amount of money for this new as they are basically no longer made but you can snag them pretty cheap used)

1 Mackie HRS120 subwoofer (also no longer being made but I found one B-stock somewhere) ..

Basic 5.1 setup

These are all THX certified reference studio recording gear. The basic idea is if its good enough to record w/ its probably good enough (w/ some modification) to play back on.

The 824's are relatively cheap even now.. I think the modern equivalent of this (if I didn't have the 824's already) would be tannoy's which are equilizable individually at each speaker and have center channels still built. The idea of calibrating for the room at the speaker level is pretty genius actually. I don't know much else about it but Tannoy's blurb from when I was hunting for a center channel.

A M-Audio 410 24/96 DA. Basically for our purposes its a 10 channel D/A converter running 24/96. The DAC on here is actually pretty good (or was pretty good a few years ago when I bought it). Regardless its a seemless upgrade to any new DAC as they come out which isn't really possible on a preamp.

A spare macbook pro 2.6 ghz Dual Core Laptop.. This is a pretty new machine and I happened to have a spare one. The mac laptops are pretty quiet .. or at least quiet enough for apartment living so would make a reasonably good preamp. (its way quieter than the PS3 for a point of reference).

Running this on a mac probably isn't the smartest idea because of the lack of blu-ray support. but I like the aesthetics and use the PS3 for blu-ray for now (w/out 5.1 but I think I can work that out by feeding the PS3 back to the maudio via fiber).

I've mucked about with VLC and XBMC and Plex to serve as the front end and I am using a Spyder 2 Pro to calibrate the TV Screen (I use this normally to calibrate my monitors).


Here are my thoughts

(1) Cheapish *proper* calibration of any TV via Computer monitor calibration and ICC profiling is a definite advantage of using a computer as a dvd / video player as the color matching is way more rigorous than simply tweaking settings on a TV.

(2) Upscaling is way better than TV upscaling (Samsung 5271) and is equivalent to PS3 upscaling (which is pretty amazingly good), I don't have a receiver upscaler to compare it to.

(3) Its nice to have the Hulu / Youtube / Netflix /Internet Radio integration but its a bit hacky to go between eyetv (cable tv) but w/ eyetv its a free DVR basically. Once the software stabilizes, it probably can be setup so its reasonably straightforward to choose btwn a few options (w/ an iphone remote or that weird apple remote something)

(4) In *theory* because the dolby decoding is being done in the software as long as you have enough speakers, its future proof as far as audio / video codecs are concerned. The TrueHD ffmpeg codecs are being worked on now and I believe are in ffmpeg now. Another obvious one is the net-codecs don't need another conversion to AC3 to be sent a receiver for translation. There are certain issues w/ TrueHD and Blu-Ray and HDMI encryption but I hope this will get sorted out but who knows, the linux (and via ports mac/windows) guys are pretty amazing so its quite possible this may get sorted out.

(5) I really like the fact we can use the spyder to ICC profile the TV (which is way better than using TV calibration methods) and modify the video output to match the ICC profile via the software.

(6) Speaker compensation / Profiling software is not there yet. That said XBMC and VLC are open source.. it would be pretty easy to send pink noise / white noise / detect the input (with a profiled microphone) / and set up audio filters on a per channel basis. Even though its not here now (as far as I can tell), I think this has more potential than the current Audyssey route because you can stare at the curves and reset them to something you like once you've profiled your speakers.

Its a bit like the DEQ-2496 (I have one of these now and have used them in the past for just this and was thinking of throwing two (maybe 3) of these into the chain as a poor mans speaker profiler, and simply doing overall leveling/delaying on the maudio side). I'm not a big fan of doing a needless ADDA to be honest so would rather doing this earlier in the chain. (*If* one could find a cheapish 3 toslink output box one could do this w/out the ADDA)

(7) I think there are some issues w/ the Mac setup and bit-correct outputs. I don't know if this is Mac specific issue, or an issue in general. But the DAC output is fixed as far as I can tell (in Audio Midi) This means if you send output to a rate that is different from that, I *believe* the software is doing another conversion to the DAC rate. If DACS aren't forced to be fixed and can do any bit/freq. rate it would be far better to set the DAC dynamically. The "hack" for now is simply keeping it at the highest or the standard bitrate that most movies are set to.

(8) Right now the Active speakers are set to auto on however this doesn't seem to work w/ the MAudio 410 box as it apparantly sends a signal as long as its plugged in w/ the firewire (even w/ the machine off). This is vaguely annoying as you have to run around turning off/on speakers.

(9) I've always loved Mackies .. super clean at all volume levels. I've never used them for "watching tv" .. its pretty genius .. seriously :)

Anyway I am curious if any of you guys have tried something similar w/ any types of success. I dont know if I would say this is the future.. but it certainly tinker friendly :)
 
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strube

strube

Audioholic Field Marshall
I have never done it to the extent that you are talking about, but honestly, it sounds like you know pretty well what you are doing.

I don't like macs for very good reasons, and enjoy cringing when they are mentioned, but I won't be too hard on you :D.

I have been interfacing my PC and home AV systems for years, and I am a huge fan of doing such. As for using it as a preamp, sometimes I have run 7.1 analog out of the computer and into the multi-channel inputs of an AVR, which worked great, and the PC with a nice sound card had superior quality to the cheap AVR because of nicer DACs (I am sure it would have sounded better if it were run to a better amp, but my speakers in that system aren't that beefy to begin with). The sound card also has some okay EQ and other sound management stuff that the AVR doesn't, and is capable of very high bitrates (higher than any source material I am familiar with). I am sure it would have sounded even better on my main system but I have never done that - I am connected to my main system from PC to AVR via HDMI. I also have a PC directly connected to the TV which also works great for the Netflix/HULU/etc. reasons you mentioned. My TV/HTPC setup is hooked to a stereo receiver and speakers via analog cable. Another appealing thing is that since you can soon buy CableCard tuners (either PCI-E cards or USB, for the laptop users) for your own system, you can have an HD DVR that you don't have to pay a ridiculous monthly fee for.

Technically, every time I have run my laptop audio output to my active M-Audio monitor speakers, I was using the laptop as a preamp. I think this happens all the time, and works quite well, I might add. :)
 
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B

bloosqr

Audiophyte
Yea the Macs are probably not the way to go.. but they do do standard audio reasonably well .. I am curious what will happen with regards to TrueHD. The encryption problem if it doesn't get fixed will unfortunately kill this idea of going this route..

I was wondering if you or anyone else had any experiences with putting DEQ-2496's in the chain for room correction. This is the behringer parametric / standard equalizer. They are pretty cheap ($200ish i think per 2 channels)..
 

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