PSA - Check your Motherboard Optical Sound

For the past while, I've been running sound out of my PC using the motherboard TOSLINK optical connector to run to an old surround system I have.

Recently while flying my spaceship in Elite Dangerous, I was beginning to think that my 20 year old surround system was starting to die as I wasn't hearing separated/crisp audio from the surround speakers.

While poking around the internet, I found that other people had a similar issue. We had 1 thing in common...a Realtek audio controller on our motherboards.

When I first setup the system, I used various movies to test the surround. The appropriate DTS/Dolby Digital LEDs lit while playing the movie, so I "knew" things were working fine.

On a whim, I did some Google searching and found this website: https://www2.iis.fraunhofer.de/AAC/multichannel.html

When I ran the test signals, I was not getting separate audio from my rear channels...just like I thought was going on in-game.

I played a movie, and it worked fine. So the 20 year old surround system (Kenwood) is still working great.

I was REAL close to getting a new sound card. Again, on another whim, I went out and bought 3 sets of 3.5 mm to RCA cable sets, and plugged the analog audio from my motherboard into the surround analog inputs on the surround system.

WOW...I now have full surround on my system...even in games!

What a difference!

After more research, it appears as though the motherboard manufacturers did not want to pay the Dolby license fee to encode non-movie data into the compressed digital optical format.

This is not true for all motherboards.

If you are not sure, run the test files from the website above...it will tell you for sure.

Now...it's like I'm gaming on a whole new level...I had NO IDEA what I was missing!

It's possible to use software surround encoding.
http://www.crutzi.info/xbmc-simultaneous-spdif-and-hdmi-surround-sound
You'll have to decide for yourself if the lossy encoding ends up sounding better than the losses from the added digital to analog to digital conversion.

Those with hardware that supports HDMI should simply use that.

Thanks for he post, but you missed a few key points:

1) Windows, not Linux
2) Not using XBMC (this does not play games titles)
3) Movies play fine
4) My surround system is 20 years old...does not have HDMI input. Also, while here are devices that pull SPDIF out of HDMI, I did not find any at time time that are HDMI 2.0 compliant (4K monitor). HDMI requires a video signal to pass audio.

It's if the audio needs to be encoded for the SPDIF digital optical transmission.

I bought a dual rca to 3.55 cable and after awhile started noticing noise from my tv output to my a5+ speakers. Now I just toslink from the back of the tv and usb from my pc to my dac but I only have a proper 2.1. Can't wait to mount my tv to it's wallmount and grab some speaker stands.

Yeah - if I start getting noise, I'll get a sound card.

My processor is actually showing some usage while gaming too!

Bought myself a Sound Blaster Z sound card, and installed on Saturday.

With this sound card, all system/game/movie sound comes through the optical TOSLINK connection in 5.1 surround. Validating that my mother manufacturer was too cheap to pay license fees.

The sound coming through the optical on the Sound Blaster Z was as good as the sound coming out of the analog connections on the motherboard.

HOWEVER...

The sound that comes out of the analog connections on the Sound Blaster Z sounds WAYYYYYYY better than the optical connection. Like WOW better.

The only thing I can figure is that the DACs on my 20 year old Kenwood receiver are not nearly as good as the DACs on the Sound Blaster Z.

The analog chain on my 20 year old Kenwood is still awesome. The sound is just incredible.

The software tools that come with the Sound Blaster are spot on and extremely useful. I was able to balance the audio levels properly, sub woofer crossover frequency, and graphic equalizer settings (could not do this properly with the software tools for my motherboard sound).

How does it sound in stereo mode? 5.1 over S/PDIF is lossy while stereo over S/PDIF is lossless. Theory says that the analog inputs on a digital amplifier always perform worse, but that doesn't account for lossy encoding.

Those multi channel analog inputs are becoming very uncommon nowadays. But if that's what you're after, you can actually use it in your favor by buying cheap hybrid digital amplifier units and ganging up a few to handle all the channels. Or even do a mixed config where the two front speakers use S/PDIF but the rest run analog. It's also worth noting that a receiver that old is going to have some of the early DSP algorithms so don't be surprised if a hybrid digital unit based on a recent chipset manages to outperform it.

Thanks for the feedback!

Yes optical digital signal on 5.1 is a lossy format. My statement above said that the sound coming from the digital link on the Sound Blaster is as good as the sound coming out of the analog connections on my motherboard sound card...both running to the same amp.

I don't necessarily agree with the statement that "analog inputs on a digital amplifier always perform worse". You have to look at the total signal path.

Optical:
Sound Card: Optical Out --> TOSLINK --> Amp: Optical In --> Amp: DSP Process --> Amp: D/A --> Amp: Analog Amplifier

Analog:
Sound Card: DSP Process --> Sound Card: D/A --> Analog Cables --> Amp: Analog Amplifier

Assuming "unnoticeable noise" in the Analog Cables (a valid assumption with good cables), the sound quality boils down to which D/A stage is better...the ones in the Amp or the ones in the Sound Card. The analog outputs fed into my 5.1 surround amplifier sound much, much better than the digital signal from the Sound Blaster (and the analog signals from my motherboard sound card.)

My old Kenwood produces fantastic sound. (This unit is so old that the "high tech" video switching inputs are S-Video! Who remembers S-Video? Hehe)

I tried just stereo and I cannot tell the difference between optical or analog. When I say it sounds better...it much more of a full surround sound experience...deeper low frequency, richer middle frequencies, and more crisp high frequencies.


The while "journey" with this post was realizing that the optical output of my motherboard was only sending 5.1 data when movies where played...not for anything else in Windows. I got around this by running the analog cables from the motherboard.

My hopes with the Sound Blaster card was that I would be able to output digital 5.1 surround data for all situations in Windows. This worked...and the sound quality was as good from the Sound Blaster optical as from my motherboard analog. This indicates that the D/A converter stages on my motherboard are "as good" as the D/A converter stage on my 20 year old Kenwood surround receiver.

However...the analog sound out of the Sound Blaster is just incredible. By inference, the D/A converter stages on the Sound Blaster card are superior to the Kenwood receiver and the motherboard.

The "DAC" (Delta Sigma modulator) in a digital amplifier is never bypassed. At the end of the following page is a block diagram of a digital amplifier, with plenty of theory before it:
http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html
Note that the input to the Delta Sigma modulator can be either analog or digital, but the implementation (opamps vs. digital logic) is very different. It's pure digital if it's digital in and hybrid digital if it's analog in. (The latter has some of the benefits of a digital amplifier with native compatibility with analog equipment, but doesn't reach the ultimate SNR that can be achieved with a modern pure digital design.) While it's possible to make an amplifier that has both types of modulators and switches between them, I have never come across one. The usual way it's done is by adding ADCs for the legacy inputs, reusing the DSP logic used for equalization and effects.

I think we might be talking past each other here.

I am not talking about the actual technology of the D/A converter (or DAC as it is sometimes called). A Delta-Sigma converter is just one type...there are also successive approximation, switched, etc. I am talking about the various amplifier / pre-amplifier circuits that are present around the D/A converters (and A/D converters for analog inputs like line-in and mic.)

However, the most common used D/A technology in audio is the delta-sigma type due to it's low cost, high bit-depth, and built in anti-aliasing filters. Of course the trade off with this type of technology is, as always, group delay (i.e. how long it takes for a change in the digital input to appear on the analog output.)

I would never use a delta-sigma type D/A or A/D in an application that was part of a real-time control loop...as the signal group delay could add to system instability...if the group delay is on the same order of magnitude as the fundamental responsive frequency of the item trying to be controlled.

While I have never actually designed a PC sound card, I have designed numerous related systems over my career...in addition to my Master's Thesis. I put together a quick block diagram of what I was referring to:



This diagram is probably not 100% accurate, but it does represent a conceptual view of what is happening.

As the audio quality with my system is the same when using the analog output of the motherboard sound vs. the optical TOSLINK of the Sound Blaster...this infers that the D/A converter in my Kenwood amp is at least as good as the D/A converter in the motherboard sound...as the main speaker amps are constant in both configurations.

As the audio quality with my system is better when using the analog output vs. the optical TOSLINK of the Sound Blaster...this infers that the D/A converter in the Sound Blaster is superior to the D/A converter within my Kenwood amp...as the main speaker amps are constant in both configurations. This makes sense as this unit is 20 years old.

(Note: the 5.1 audio digital optical format in the TOSLINK data is lossy, and could be contributing to some of this as well. I say TOSLINK to keep is simple...for me...as I always forget the official acronym used - hehe).

Nevertheless, the power amps in the Kenwood amp are still very good!

I hope this makes sense!

A digital amplifier runs a bitstream into the power electronics, with a few stages of level translation to drive the output MOSFETs or IGBTs. Here's a datasheet of a HVIC inside a digital amplifier:
http://www.ti.com/lit/gpn/tas5631b
The bitstream is generated by the Delta Sigma converters inside the DSP. While it is possible to have a separate set of analog input Delta Sigma converters for analog inputs and switch between them as your diagram indicates, I have never actually seen that implementation being used. The main reason probably being that standalone analog input to bitstream output chips are not common while complete ADCs are. Using an analog input HVIC doesn't make sense since a digital input HVIC is cheaper than an analog input HVIC and a good DAC, plus it would be more difficult to get a good SNR. ("Digital tube amps" just use a cheap codec to insert the tube stage since the tubes themselves would limit the SNR. The point is to make it sound like a tube amp, not get ultimate SNR!)

Delta Sigma converters running at the frequencies used for audio typically have a latency of well under 1ms - not significant enough to affect gaming performance. Some DSPs effects can introduce significant amounts of lag. Particularly when it is desired to mix multiple signals with unsynchronized clock sources - trivial in analog but difficult in digital! That is why analog mixing consoles are still very common and why there's a market for high power analog input HVICs.

I understand how various amplifier topologies work...class A, B, AB, C, and D and E...and have designed with them all. Each has pros and cons.

The chip you referenced I am familiar with and have used...but notice the rev date...2010.

My Kenwood is 20 years old...it doesn't use that chip. In fact, the output power amplifier stages are class AB (I already opened it a long time ago and looked)...hence the awesome sound. The pre-amps are high quality op-amps. The power supply is a switcher, but still pretty beefy.

Now a days, you can get a chip from TI that will do 100 W per channel for 5.1 that is small, a switching topology, and doesn't require an external heat sink (you heat sink it through a "power pad" when it's soldered to the board.). All you do is slap some jelly bean components around it and you are done.

This is why surround sound systems in this power range are so cheap now...and are great for the average guy who won't mind 0.5% or so THD (or about 8-bits).

The oldest digital amplifier I have opened up was a 2003 vintage Philips. It was already using a TI DSP with the Delta Sigma converters built in along with some Philips gate drivers and International Rectifier MOSFET modules. Digital amplifiers have existed since the 80s and maybe even earlier, but haven't come into the mainstream market until the 2000s.

Yours, being 1997 vintage or so, apparently is one of those old analog designs that they bolted a bit of digital logic to so they could call it digital. Probably made a lot of sense back when almost all consumer audio equipment was analog. And it is possible to bypass the DAC on one of those because it's not really a digital amplifier.

Nowadays, digital amplifier technology has advanced to the point where they're making single chip headphone "DACs" based on it. Not so much for efficiency per se - that's insignificant when 0dBm into a pair of headphones is very loud - but rather to get rid of the opamps that use relatively large amounts of power and don't scale down to smaller processes very well. The main driver behind that happens to be USB-C smartphones. Pretty amazing how a tiny BGA chip that fits inside a USB-C plug can easily hold its own against a top flight PCM1792A+OPA1612+TPA6120A2 audiophile setup. (In fairness, the PCM1792A is a pretty old chip built on a 180nm or 250nm process, as opposed to the BGA built on a 45nm or so process. There just wasn't too much demand for standalone low power HD DACs until recently!)