[nu77]

I would like to build an HTPC to use for high-quality audio output as well as TV and DVD watching, but I don't fully understand some of the audio handling issues. I've been looking at the Lynx, M-Audio, RME and ESI cards for high-quality 24/96 or 24/192 output, but don't want to buy anything until I really understand a little more first.


1. Can you hook the output of a sound card DAC directly to your power amp? Are there any issues controlling the output level for multi-channel formats (e.g. a single volume slider that brings up all channels proportionally)? I'd like to eliminate my pre/pro if possible since it won't be providing much functionality in conjunction with an HTPC.


2. For DVD playback, how can I perform Dolby Digital and DTS decoding? Is this done by the DVD player software, or does it have to be a function of the sound card?


3. How can I get a "matrix" mode for synthesizing rear-channel information from 2-channel stereo input? (e.g. my pre/pro does this now).


4. If I do need to keep my pre/pro for DTS decoding or other reasons, what do I need for digital audio passthrough? I've heard that SPDIF only handles 2 channels, not 5.1.


5. Can DVD Audio decoding be done by DVD player software, or do you need a card like the Audigy2 to do this?


6. Are there any motherboards with build-in audio that will allow uncorrupted 5.1 digital passthrough? What is AC97 (I assume it's low-quality and should be avoided).


7. I've heard a number of people claim that digital-to-analog conversion really has no place inside a computer cabinet because of all the spurious electrical noise there. I can't help but feel this is bunk and audiophile elitism for a number of reasons: (1) many musicians and recording studios have moved over to complete PC-based digital recording with high-quality sound cards without sacrificing quality, and (2) many sound card tests have demonstrated excellent quality results from sound cards measured in PC environments -- low noise, jitter lower than many audiophile components ( http://www.pcavtech.com/soundcards/compare/index.htm ).


8. I've heard that when using an ATI All-in-Wonder video card, it isn't possible to send the TV tuner's audio bitstream to your sound card's DAC for analog output. You're stuck with sending the digital audio out the AIWs outputs. Can anyone confirm that?


9. Is there a good primer on configuring PC audio, sound cards, drivers and applications?


Thanks very much,


Nu

 

[Chris White]

My $.02 worth...


1. AFAIK, no, you can't, nor would you want to. In nearly all cases, the dacs in your pre-pro would be better than the dacs in your sound card.


2. Use the SPDIF output of the sound card and let your pre-pro decode.


3. Don't know.


4. Incorrect. SPDIF wlll pass 5.1.


5. I'm not aware of a sound card that will decode dvd-audio.


6. I'm not aware of any mbs with on-board audio that is 5.1 capable.


7. I don't think the problem is digital to analog conversion inside the pc per se. The problem is the quality of dacs in audio cards (see answer to first question).


8. Don't know.


9. You can learn pretty much anything you need to know on these subjects if you spend enough time searching this forum.

 

[Goi]

1) You can, but you probably won't want to for reasons that Chris White has already mentioned. Its better to treat your HTPC as a DVD/CD-player than a prepro.


2) AFAIK, almost all cards can only do it by software, only some Creative models can do it in hardware. High-end/Audiophile audio card manufacturers usually cater more towards the professional recording market than the audiophile/HTPC market.


3) Some cards have certain modes that allow the rear channels to be utilized when playing stereo material. This is soundcard specific so there's no definite answer on how to do it, or whether you're able to do it at all.


4) S/PDIF is what you need. S/PDIF handles 2 channel PCM audio as well as compressed DD/DTS 5.1 sound, even DD-EX and DTS-ES. There's enough bandwidth in S/PDIF to do that, but not enough to do DVD-A and SACD.


5) You need the Audigy2. There might be hacks to allow DVD-A playback on cards that have at least 6 channel output now or in the future, but I don't know of it right now. AFAIK, only the Audigy2, with its specific software player, is able to do it now.


6) Yup, lotsa motherboards now come with built in audio from Crystal/Realtek/Analog Devices/CMedia that support S/PDIF output, which is really all you need for 5.1 digital passthrough. AC97 is simple a specification/format that calls for 16bit/48KHz output, among other things. It should be avoided as far as possible, since CD material is 44.1KHz, and the upsampling process on the majority of AC97 cards/chips are not that good. None of the high-end/audiophile/recording cards comply to the AC97 standard.


7) Not too sure about that, but then again you have to realize that the computer is REALLY a very noisy place when it comes signals, so there might be some truth to that. Not much within a computer is shielded, so you have signals flying everywhere. Whether it matters is another question that's open to debate.


8) Don't have an ATI AIW so I don't know


9) Try the HTPC FAQ?

 

[_K_C_]

Have a read through the Revo thread (it's long!) and you'll get some views on some of the questions (1,2,4,5 and 7)


I asked a similar question to your (1) at:

http://www.avsforum.com/avs-vb/showt...27#post1586727


and got slightly different responses to the ones you have here. One reply, for example, compared the M-Audio soundcards' quality to receivers in the $1200-$3500 range. I suspect this is controversial

 

[stylinlp]

I dont have the answers to any of your questions except number 7 from an audiophile standpoint. Nothing is better quality than analog. If you go shopping at any of the high end audio stores you will see that the more expenisive items are tube amps and vinyl record players. I know someone with a 100k turntable system. I myself have a $1500 table.


The recording industry today only care about their profit margin. CD's are cheap to make and record. Its much simpler and cheaper to record one of these new no talent flash-bang artist in digital than analog. Most (some have no control over the label) good artists will release vinyl. Sheryl Crow and Bob Dylan to name a few. Sheryl Crow herself stated that she hates what digital does to her voice.


I beleive that the digtial equipment used at high end recording studio's are dedicated equipment. The basic PC simply is too noisy without some modifications for serious recording. I know there is a whole slew of external equipment used in a recording studio.


BTW audio cables make a HUGE differance especially coming from a MRI and RFI poluted computer case. I would recomend at least Monster Cable as the low end to start with. Better yet go with Kimber Cable, AudioQuest, Norquest.

 

[Goi]

Norquest? Don't you mean Nordost?


Anyway, the digital vs analog debate has been beaten to death. The problem with comparing vinyls to CDs is that most recording studios don't master the CDs as well as they should, which means the final product turns out to be decent on a boombox or discman, but screwed up on higher end audio equipment. If the producers bother to put in more effort into their mastering, there's still a lot that can be obtained from the 16bit/44.1KHz PCM CD format, much less newer digital formats like DVD-A and SACD.

 

[transhuman]

Isn't it funny that the only people really concerned with $2000 cables are the audiophiles? In a studio, if you were to try any suggest such a thing, you'd be thrown out. It's all about the microphones and mic-pre-amps in the studio. Cables are cables as long as they're shielded properly and not bent or otherwise mistreated. Granted, the shorter the better for signal strength and no RF interference.


On another subject, I just purchased an Aardvark Q10 24/96 unit. It's excellent for inputing outboard audio signal to the PC. It will accept XLR and 1/4" balanced inputs on 8 channels. It's really more for multitrack recording, but I could see it being used fot HT as well.

 

[Colin Banfield]

Quote:

Originally posted by nu77 1. Can you hook the output of a sound card DAC directly to your power amp? Are there any issues controlling the output level for multi-channel formats (e.g. a single volume slider that brings up all channels proportionally)? I'd like to eliminate my pre/pro if possible since it won't be providing much functionality in conjunction with an HTPC.

Yes to all of the above. A lot of us in this forum are already using an HTPC this way. However, only M-Audio line of cards have been tailored for this purpose, with individual channel volume control & bass management. The new Revolution card is even move geared for HT use with Circle Surround II added to the other features mentioned. The measured specs on the new 24/192 DACs in the Revolution are superior to those found in many mid-priced receivers.

Quote:

2. For DVD playback, how can I perform Dolby Digital and DTS decoding? Is this done by the DVD player software, or does it have to be a function of the sound card?

Decoding is done in the DVD player software.

Quote:

3. How can I get a "matrix" mode for synthesizing rear-channel information from 2-channel stereo input? (e.g. my pre/pro does this now).

Either WinDVD or PowerDVD can do Dobly Pro Logic II. The Circle Surround II option in the aforementioned Revolution card performs this "matrix" function also.

Quote:

4. If I do need to keep my pre/pro for DTS decoding or other reasons, what do I need for digital audio passthrough? I've heard that SPDIF only handles 2 channels, not 5.1.

Well, as mentioned above, the software player can handle the DTS decoding, but to answer the second part of your question, SP/DIF can handle 5.1 from DD or DTS tracks. However, SP/DIF does not have the bandwidth to pass DVD-A or SACD content (not to mention the legal implications).

Quote:

5. Can DVD Audio decoding be done by DVD player software, or do you need a card like the Audigy2 to do this?

M-Audio plans to release a DVD-A player in January, 2003 for some of their cards.

Quote:

6. Are there any motherboards with build-in audio that will allow uncorrupted 5.1 digital passthrough? What is AC97 (I assume it's low-quality and should be avoided).

Forget about on-board sound for HT use.

Quote:

7. I've heard a number of people claim that digital-to-analog conversion really has no place inside a computer cabinet because of all the spurious electrical noise there. I can't help but feel this is bunk and audiophile elitism for a number of reasons: (1) many musicians and recording studios have moved over to complete PC-based digital recording with high-quality sound cards without sacrificing quality, and (2) many sound card tests have demonstrated excellent quality results from sound cards measured in PC environments -- low noise, jitter lower than many audiophile components ( http://www.pcavtech.com/soundcards/compare/index.htm ).

You're absolutely correct. Forget everything you've heard. It was only ever true with low quality gaming cards anyway.

Quote:

8. I've heard that when using an ATI All-in-Wonder video card, it isn't possible to send the TV tuner's audio bitstream to your sound card's DAC for analog output. You're stuck with sending the digital audio out the AIWs outputs. Can anyone confirm that?

I'm not familiar with the AIW, but couldn't you use the analog output from the AIW for this purpose? You'd connect this output to the analog input of the soundcard. Alternatively, if the soundcard has an SP/DIF digital input, you should be able to connect the digital out from the AIW to the digital in of the soundcard.

Quote:

9. Is there a good primer on configuring PC audio, sound cards, drivers and applications?

Let me know when you find one

 

[Colin Banfield]

Quote:

Originally posted by transhuman Isn't it funny that the only people really concerned with $2000 cables are the audiophiles? In a studio, if you were to try any suggest such a thing, you'd be thrown out. It's all about the microphones and mic-pre-amps in the studio. Cables are cables as long as they're shielded properly and not bent or otherwise mistreated. Granted, the shorter the better for signal strength and no RF interference.

transhuman, I've not been able to figure out this one either i.e. people willing to spend thoudsands (or even several hundred) of dollars on interconnects to play back stuff recorded using cheap cables. For example, you could buy 50 ft of quad MIC cable (standard studio cable) for about $30 . One foot of Kimber interconnects can cost you $79 or more. Like you said, spending tons of money on cables is unheard of in the recording studio. I think it just means that the Pros are smarter than the consumers who haven't yet figured this out.

 

[nu77]

Thanks everyone! It's really great to be able to run these questions by a community of users, and compare notes. Let me just summarize what I've heard so far:


1. HTPC as pre/pro -- Everything from "don't do it" to "yes, definitely." It seems that the answer mostly relates to question 7, so I'll summarize that there.


One follow-on question I have on this relates to analog vs digital volume controls. I've heard that "good" DAC/preamp solutions will do the volume control in the analog domain so that they can maximize the number of bits of resolution of the digital signal. Digital volume adjustments end up scaling the digital signal down to very few significant bits, and operating in the low-order bit (nonlinear?) region of the DAC. I believe I've mostly heard this in conjunction with 16-bit audio signals, so I'm wondering if it's an issue for 24-bit sound cards that have 50% more resolution to play with to begin with. Has anyone noticed (or better yet, measured) "graininess" or nonlinearities at low volume levels?


2. DD/DTS decoding -- S/PDIF to pre/pro to decode, or decode with DVD player software (and send multiple channels to the sound card unencoded for D-to-A conversion, presumably).


3. matrix mode -- "Depends on the sound card." WinDVD and PowerDVD will decode Pro Logic, but I'm not sure if that will work for 2-channel CD audio (presumably not, since I belive that Pro Logic must be encoded in the recorded signal). The (forthcoming) M-Audio Revolution card will do Circle Surround II which is a form of matrix mode (I think this is what my Proceed pre/pro does).


4. S/PDIF digital passthrough -- S/PDIF will pass through DD and DTS, but not DVD-A or SACD due to the data rate involved (and if I'm not mistaken, because the industry doesn't want to give access to a pure digital stream for these formats).


5. DVD-A decoding -- Audigy2 is the only way to do this now. M-Audio may provide DVD-A decoding software in January. However, I've heard that the Audigy2 is to be avoided due to the fact that it upsamples 44.1khz CDs to 48khz internally, destroying the signal quality in the process (at least from the audiophile perspective). (And from the DVD-A discs that I've heard (with choruses mixed to the rear channels, etc.), I'm not sure why anyone would want DVD-A anyway.)


6. Mobo audio -- If you're using the outboard pre/pro approach, any mobo which can output a digital (S/PDIF) signal correctly will work just fine. If you're not using a pre/pro, the sound card quality is critical. AC97 should not be used for this (although it's not clear to me whether AC97 is fine for digital pass though to S/PDIF for the pre/pro approach).


7. sound card vs. outboard DAC -- This is the most controversial issue, whether any sound card will measure up to an audiophile DAC (and I'm thinking "Stereophile Class A" here). However there does seem to be some agreement that the quality probably exceeds most mid-fi audio gear.


I've heard in numerous threads the phrase "computers are a really noisy environment" and this resonates with high-end audio gear mindset that carefully separates noisy stuff like power supplies from analog signal processing (e.g. Levinson No 32 preamp), or the DAC from the transport (No 360S and No 37). However, in carefully reading the specs, I just don't see evidence of this noise assertion. For instance, the LynxTwo has a truly amazing 115db signal-to-noise ratio (measured by PCAVTech), -133db jitter distortion, and 129db of dynamic range! In comparison the Mark Levinson No 30.6 "reference" DAC has 105db S/N ratio, and 98db dynamic range. Now granted, the Levinson specs are excellent too, but if the sound cards still aren't up to the Class A level, what exactly are we missing here? Departure from linearity? Noise injected after the sound card measurements? (I don't think so.) Lack of marketing hype?


8. AIW audio output -- I discovered this thread which is very informative: http://www.avsforum.com/avs-vb/showt...ight=AIW+audio

There was one suggestion to route the analog output of the tuner card to the analog input of the sound card, but I'd really rather not redigitize anything.


9. primer on audio -- Suggestion to try the HTPC FAQ (which I did, but really didn't get what I wanted). I guess it's time to learn by doing.


Thanks again everyone for all your help,


Nu

 

[Colossus Ex]

Quote:

Now granted, the Levinson specs are excellent too, but if the sound cards still aren't up to the Class A level, what exactly are we missing here?...Lack of marketing hype?

Best explanation I've seen so far.

 

[thomaspf]

The analog volume control is indeed an interesting issue. Fitting an analog pot into a sound card is a bit tricky. On external units like the 1010 or the WAMI rack, however, an analog volume control should be no problem.


I add a recent addition to the external DACs with exceptional measurements (unless you count weight an important audiophile necessity which might make the Mark Levinson win). This unit has the added benefit of being almost immune to digital jitter which is the problem that might degrade your sound if your digital clock is not extremely stable.

http://www.benchmarkmedia.com/digital/dac1/default.asp


This brings me to the other reason of my post. If electromagnetic interference would be a big issue with computer cards this would manifest itself in the noise measurements. Most commonly these are combined with total harmonic distortion THD+N.


If I understand this correctly the level of THD+N describes at what level the distortion and self noise of a DAC starts interfering with the actual signal. I think about it as the sound from a badly tuned radio station. Since the noise is statistical in nature you can still make out what people are saying even if the noise is very high but it clearly takes away from the signal quality.


Manufacturers like to state THD+N in % vs. the db rating for SNR and DR to make it harder to put them in perspective. Well, you can easily translate them and see at what levels the noise is starting to interfere with the signal.


THD in dB = 20 * log(THD in % / 100) - and that’s base 10 log


By going with the rough 6db per bit it is instructive to look at how many bits of a clear signal a component really can provide. When you turn on or off a bit in the PCM samples your DAC will output a slightly different voltage. The lower the bits the smaller the change. At what point can't you tell the change in voltage due to turning on a specific bit from the noise generated by the device. This should also give you a little more to think about the analog vs. digital volume control.


SNR: 107db THD+N: -90.5= 15bit M-audio Revolution

SNR: 117db THD+N: -97db= 16bit Lynx StudioTwo

SNR: 105db THD+N: -100db= 16.5bit Mark Levinson No. 30.6

SNR: 112db THD+N: -100db= 16.5bit RME Digi 96/8PAD

SNR: 116db THD+N: -106db= 17.5bit Benchmark DAC1

SNR: 118db THD+N: -116db= 19bit Orpheus One (Anagram Technologies)


It looks like that sound cards with the DACs mounted inside a PC do indeed have a somewhat harder time with noise although for some reason the manufacturers with the exception of RME (which shows in the measurements) have chosen noisy DACs for their boards. I am looking forward to the next generation products from M-audio and RME.


Does this make sense to you guys or am I completely off here?


Cheers


Thomas

 

[nu77]

Thomas,


That's really useful information. Thanks for helping to demystify what's going on behind the numbers. So the next obvious questions is: What's the advantage of a 24-bit DAC if there's only 15-16 bits of accurate information there (or what are those "extra" 8 bits doing anyway)?

 

[thomaspf]

Hi nu77,


these measurements are not done in a steady state. If you output PCM samples with all the same values that would not give much sound. So the way to think about this is more like this.


While you are playing out your samples the voltages coming out of your DAC will be a little off but only at unpredictable times and with varying deltas. The highest level of noise corresponds to your THD+N rating. So you can still hear the intended signal much like with a badly tuned radio station but the signal is overlayed with noise.


Therefore, you can hear the difference between a 16bit and a 24bit signal even if you DAC only produces 16 clear bits.


Since you brought up Mark Levinson I recommend you look at the THD+N rating of their amplifiers. Their solid state designs have levels of noise and distortion that are almost non sensical. It is just a matter of how much you like that specific noise and distortion but 24bits probably do not make sense over that kind of equipment.


However, as the THD wars around amplifiers in the seventies have shown. Low THD is a necessary but not a sufficient criteria for good sound.


Thomas

 

[nu77]

Hi Thomas,


Thanks again for the info. I'm not sure what you mean by "If you output PCM samples with all the same values that would not give much sound" but I understand in general what you're saying. The THD+N rating tells you how much of your output signal isn't "perfectly" reproduced. However, it doesn't seem to say how badly distorted those signals are that are below the THD+N floor (i.e. exactly how badly tuned is that radio really). I guess this is where you'd have to look at a graph since it's bound to be frequency dependent.


About amplifiers: I've looked at some specs as you suggested, and noticed that no one gives THD+N ratings for them. There are THD ratings, but these seem to be used to determine when the amp is clipping, e.g. the Pass X600 outputs 600W with 1%THD. Only Krell publishes specs like 0.03%THD @ 1khz, 0.16%THD @ 20khz. Nonetheless, I understand that your point is that even 16 bits of clean output (96db) from your DAC is quickly lost on your amplifier.


Finally, thanks for the pointer to the Benchmark DAC1 ( http://www.benchmarkmedia.com/ ). I wasn't aware of that unit before, and it looks very good. Also, the Orpheus One DAC ( http://www.orpheuslab.com/orange/are...rpheus_one.htm ) has a 0.00055% THD+N rating for 24/44.1k signals which equals 105db or 17.5 bits, not 19 bits (or at least they don't give a spec for 24/192).


Next question: How does the SNR relate to THD+N rating? E.g. how does a 116db SNR relate to a -106db THD+N (as in the DAC1 case)? Is that 10db difference a measure of the "bad radio tuning," or is it the point where you can't hear the signal at all. I could have sworn that I've seen specs where the THD+N rating was less than the SNR, so that doesn't really make sense.

 

[thomaspf]

I will respond to your SNR question when I have more time later but for contemporary solid state amplifier design you might want to look at.

http://www.bryston.ca


and if money is less of a concern

http://www.halcro.com


These companies actually publish their THD+N rating at clipping over the full frequency range. And that is for a reason.....



Thomas