Vista Audio Playback, Part 2

I've been pretty busy lately, so haven't had time to post any articles. Earlier today I received a nice email from someone (won't mention names unless I have permission) who's also a big HTPC proponent. He mentioned that he's been following Amplio Audio and anxiously awaits updates on our amps and our next article about Vista audio playback. Well, that was the kick in the ass I needed.

BTW, if you read an article that you would like me to follow up on, or have any questions, please feel free to use the comments at the end of the posts. I realize that most people are comfortable with email, but I'd like to see these articles become more of an open conversation that anyone can contribute to.

Anyhow, back to the topic... In the original Part 1 article I mentioned comments I read in a thread on diyAudio titled "Is Vista really capable of bit perfect output?" The original poster started by explaining that the sound quality when playing audio/music with his computer was better than using his expensive dedicated audio components. There are a couple of reasons some may believe a computer based audio system can never sound as good as dedicated stand-alone components. One is that the computer is just too electronically noisy to pass an analog signal without some distortion. The second reason is that the computer software and/or operating system modifies the audio data before passing it to the soundcard and DACs, thus distorting and/or damaging the sound quality.

There are several ways to avoid the first problem. One is to purchase a good quality soundcard that is properly shielded from any electro-magnetic interference. The other is to use a product who's analog circuitry is external to the PC. All FireWire and USB based soundcards fall under this category, as do a new generation of USB DACs. The product Amplio Audio is working on falls under this category as well. Up to this time, we have been using FireWire and it still proves to be the best technical solution.

The second problem is a little more complicated. Sound degradation caused by the operating system was true with Windows XP and standard WDM drivers. XP's audio engine relied on a mixer (KMixer) that would resample all audio to 48 KHz so everything output from the PC would use the same sample rate. There are some ways to avoid resampling, but if you adjusted the volume or simultaneously allowed sound output from other applications (including system sounds), resampling was performed. That means the CD's 44.1 KHz sample rate was always converted to 48 KHz. Another problem with this audio engine was that to lower the sound volume, the data was simply truncated to a lower resolution. So 16 bit audio was reduced to 14, 12 or 10, etc., bit data to get a lower volume. This can dramatically decrease the sound quality.

This is where the thread then moves on to the bit-perfect discussion. To avoid degrading the sound by modifying or truncating the bits, you could use a driver like ASIO that bypasses the Windows audio engine so that the original source audio data is not changed all the way to the DACs. This is how you could get bit-perfect output. Of course the software players had to provide support for these sort of drivers. Windows Media Player or Windows Media Center do not. So you had to use other players like J.River's Media Center, Winamp (with a special ASIO plug-in), Foobar, etc., to achieve bit-perfect performance. Now with Vista, a couple things have changed. First, the audio engine is much better. Even if the audio is resampled, the algorithms are much better and the effect on sound quality is not nearly as bad as what happened in XP. They've also improved the volume control so that they no longer truncate the bits to reduce sound levels. Instead, it converts the data to 32-bit floating point, then performs the volume adjustment calculations and then converts back to the original sample rate. This basically gives you lossless attenuation. It's not bit-perfect, but there is no degradation in sound quality. Some dedicated audio hardware that uses high quality DSP chips use this same technique. For the purist, who still want bit-perfect operation, they can still use ASIO drivers if they've been updated to work under Vista. These drivers will also bypass the audio engine, just like they did with XP. Vista also supports a new feature called "exclusive mode". Exclusive mode also bypasses the Vista audio engine and will provide bit-perfect playback. However, you need an application that supports exclusive mode and most I'm familiar with, like J.River Media Center, Windows Media Play, Vista Media Center, Foobar, etc., don't.

Getting back to the diyAudio thread, the bit-perfect discussion mentions that there is a newer software player, called XXHighEnd, that uses Vista's exclusive mode. There's another program called XMPlay that can run in exclusive mode when using a WASAPI output plugin. The sound output from a program using an ASIO driver or running in exclusive mode should be identical, because bit-perfect is bit-perfect. However, several people, including the original poster and the developer of XXHighEnd (not the same person), claim that XXHighEnd sounds better than other bit-perfect solutions. In fact the original poster was also a big fan of using Foobar with ASIO drivers, and he claims the sound has improved a lot when using XXHighEnd. When asked how something that outputs the exact same data can sound better, the developer doesn't provide any answers that satisfy the skeptics. The closest he comes to any technical explanation is that he does something to minimize jitter. But that doesn't make much sense given the way the audio chain works. If the audio data is buffered and the DAC is driven by a local clock, the audio software player shouldn't have any effect on jitter. He also admits that he doesn't know why it sounds better, but that there are many ways a software application can have an effect on the audio quality and he's just been tinkering around trying to find the best sound quality. That's where things get confusing to me. Or as another poster/skeptic put it:

1. It's bit-perfect
2. PCM needs to be processed some special new way to sound best
3. No, it's bit-perfect
4. If you were to, say, play a byte later in the stream than it was originally, that might be useful
5. No, really, it's bit perfect!
6. You're mucking around with the data based on some theories you have that you won't explain and if we don't just accept that it is bit perfect and magically sounds better than we are just mean, old unbelievers.
7. Oh, and it is bit perfect.

The developer of a kernel streaming (KS) output driver, which is also achieving bit-perfect performance like ASIO drivers, compared the output from three different bit-perfect solutions - Foobar2000 with his KS output driver, XMPlay running in exclusive mode and XXHighEnd running in exclusive mode using it's third engine. Using an oscilloscope, he found that the output was identical. They are all bit-perfect. He also says he cannot hear any difference, so he doesn't recommend the XXHighEnd software because they charge for it (and Foobar2000) is free, the user interface is pretty weak and the program is immature. Like I said, others, including the original poster, claim it sounds better.

I have to admit, if it sounds good to you, I'm not going to try to convince you otherwise. I'm also not convinced bit-perfect output is the only acceptable way to listen to audio. Especially since Vista is not bit-perfect, unless you use exclusive mode, but it still sounds great because any changes are lossless.

Vista Audio Playback, Part 1

I've been following this thread on diyAudio Forums titled, "Is Vista really capable of bit-perfect output"? There are some comments that I thought readers of my blog might find interesting. As you can see I added Part 1 to the title of this thread. I don't know if this is really going to be a multi-part article, but what the heck, I'll add it to the title just in case.

The original poster starts out by telling us what audio equipment he's using. He has a PC running Vista Ultimate. For the PC's audio, he has a MOTU 896HD sound card, which is an 8 channel 24/192 audio interface that costs around $1,000. This is connected to his PC via a FireWire connection. He uses the digital AES/EBU outputs of the MOTU to connect to the digital inputs of his Esoteric D70 external DAC. Esoteric, which is a division of Teac, doesn't look like they still sell the D70, so I couldn't find a link to their product information. Anyhow, it is/was a pretty highly regarded $6,500 stereo DAC. It's a shame that he's only using 2 channels from his multichannel MOTU interface. Next, the analog output from each channel of his D70 are sent to Pass Labs XVR1 active electronic crossovers. Each of these babies normally cost $5,000. Each crossover is taking a input signal and dividing them into high-pass and low-pass outputs. For a stereo system, you normally have the left and right channels feeding a single XVR1 and it outputs the low frequency and high frequency signals for each channel. So that is two channels in and four channels out. In this case, since he has 2 XVR1s, I assume he is splitting it up so that the left and right channels are each getting 4 output channels. These 8 outputs are connected to 8 Hypex UcD700 amp modules. So that's 4 amp modules per channel. I have no idea how much he paid for his amps, but that's a lot of power. Each one of these UcD700s provide 700W rms power. That's 2,800 Watts per channel. Most likely, this was a diy project. It might not be as expensive as a commercial product with similar performance specs, but based on the other components in his system, I doubt he scrimpted on the parts for his amps. Just to give you an idea of the price of a couple components he probably included, the amp module and matching power supply for the UcD700 cost up to $500 and $350 respective (using the current exchange rates). Since he probably has 8 of each, just those components cost $6,800. Next add in the transformers, interconnects, chassis, etc. and his amp probably cost at least $7,500 - $10,000. The amps are feeding a pair of Wilson Benesch Chimera loudspeakers that cost somewhere between $21,000/pair and $33,000/pair, depending on your source of information. So, if price is a determining factor, this approximately $50,000 sound system must sound pretty damn good.

Now why would someone connect a PC to a high-end system like this instead of an expensive high-end audiophile CD, DVD-Audio, or SACD transport? Actually he does own one of the $7,500 Esoteric P70 transports, but still prefers the sound through the PC. When asked if the PC chain was really better or just different, he responded that it was definitely better. Then he gave an example of a test he performed to compare the sound of a CD playing from his P70 transport to the sound of the same CD ripped as a WAV file to his hard drive and the same song downloaded from Linn Records website in a 24/96 FLAC file. He said, "When played through Foobar, the FLAC version is simply stunning. The Wav version is very good, though flatter than the FLAC. The CD played through the transport sounds more edgy, less fluid and less solid." Then someone responded that there must be something wrong with his transport because he has a modded version of the same one and it sounds perfect. To which, our original poster responded:

"I agree, the standard P70 is a stunning transport. I've not heard any modded versions, so can't comment on their performance."

"I don't think there's anything wrong with my transport though. It's dead silent when playing CDs and handles (my wife's!) badly scratched CDs easily. It literally blows my Pioneer DVD, acting as a transport, out of the water. No, I'm pretty sure it's doing a sterling job, given the constaints of the ancient 'red book' standard."

"But as you yourself admit, the standard P70 is not perfect. You reckon that the modded version sounds "even more relaxed, richer and bigger". Well, I reckon you get all of this (and maybe more?) by extracting and playing wav/flac files well."

"As for 24/96 FLAC files, I'd venture that no transport on the planet, modded or not, comes anywhere close to the sound quality you can get from them. If more and more companies start offering these downloads, I think the audiophile community is simply going to have to start taking more of an interest in PC music."

I guess I will make this into a multi-part article, since I'm going to go ahead and post this now and then continue with the discussion about Vista playback in the following parts.

Microsoft Responds to Vista Audio Problems

Last week's post, 'Networking problems when Vista Audio is Active' linked to reports from the 2CPU forums about networking problems in Vista during audio playback. Adrian Kingsley-Hughes in his "Gear for Geeks" column for ZDNET received a response from Microsoft regarding these problems. You can just read his article, but I might as well provide his list of Microsoft responses here:

• “We have been looking into this problem and are working on a doc that will go into the technical details of what we have found.”
• “Please note that some of what we are seeing is expected behavior, and some of it is not. In certain circumstances Windows Vista will trade off network performance in order to improve multimedia playback. This is by design.”
• “The connection between media playback and networking is not immediately obvious. But as you know, the drivers involved in both activities run at extremely high priority. As a result, the network driver can cause media playback to degrade. This shows up to the user as things like popping and crackling during audio playback. Users generally hate this, hence the trade off.”
• “In most cases the user does not notice the impact of this as the decrease in network performance is slight. Of course some users, especially ones on Gigabit based networks, are seeing a much greater decrease than is expected and that is clearly a problem that we need to address.”
• “Two other things to note. First, we have not seen any cases where a users internet performance would be degraded, in our tests this issue only shows up with local network operations.”
• “Second, this trade-off scheme only kicks in on the receive side. Transmit is not affected.”

Seems pretty strange to me. Slight degradation? Some people have reported network performance throttled to 5-10% when playing audio. Heck, when using Windows Media Player the network performance is reduced even when the audio is paused (using other media players like Foobar2000, the network performance is only throttled during playback). Anyhow, I never had any pops, clicks or skips when playing audio on my old Pentium III or IV hardware running Windows NT while connected to a network back around 1999. So I still don't understand why they are having this problem with today's hardware. Hopefully this will be fixed in a future patch or something.

Networking problems when Vista Audio is Active

Just thought I'd relay some news about Vista audio that has been spreading around the last few days...

People have reported on the 2CPU forums that network performance is throttled whenever they play audio in Vista. It looks like more of an annoyance that a critical problem. Hopefully Microsoft will respond with a bug fix in the near future.

UPDATE 8/24: more information about this issues discussed in this AVS Forum thread.

Vista Audio - Digital Room Correction, Bass Management, etc.

In a recent AVSforum post titled, "Audio Processing in Vista Explained", Amir Majidimehr, Corporate Vice President of Microsoft’s Consumer Media Technology Group, writes about the new audio capabilities planned for Vista. New audio features included in Vista are digital room correction (DRC), bass management, loudness equalization, headphone virtualization, and channel control tools.

When asked, if after you plug your PC into an A/V receiver and perform the room correction calibration on the PC and then disconnect the receiver from the PC, 'will the receiver retain the calibration settings?', Amir replied, "Unfortunatly not. All the processing is done inside the PC and only works if you use the PC as the source, driving your receiver. Take away the PC and there is nothing there anymore. For your receiver to have similar capabilities, it would have to have a ton more hardware in it." Anil then favorably compared Vista's room correction capabilities to a high end TacT processor by saying, "The TacT processors do what you say but the one I have cost me a cool $10K and it does less in some respects than Vista!"

For a quick explanation of what DRC is and how it can benefit you and your system, check out this DRC guide.

The bass management feature is very flexible and doesn't have some of the limitations you find with the bass management on most A/V receivers. For example, with Vista's bass management, you can have any combination of large or small speakers, with or without a subwoofer. The crossover point can be set to whatever your loudspeakers need. When sending a full range signal to any of your small speakers, the portion of the signal below the crossover point will be routed to the subwoofer, or in the case of a system without a subwoofer, the lower frequencies can be routed to the large speakers.

Most A/V receivers won't let you send a full range signal to the front speakers if the subwoofer is engaged. They force you to filter out the low frequencies from the fronts and send everything below the fixed crossover point to the subwoofer. This works okay with a sub/sat system, but isn't very appealing for anyone who has large or full-range loudspeakers in the front. There are also some A/V receivers and processors that will not send a signal to the subwoofer when it is set to stereo mode. Also, with most of the A/V receivers and processors, the subwoofer output jack is low-pass filtered so any signal above the frequency setting (usually in the 100Hz-150Hz range) is blocked. Most powered subwoofers also have a built-in low pass filter, and when the two filters combine you are increasing the steepness of the filter. Too steep of a filter slope makes for worse sound. Anyhow, it sounds like Vista's bass management feature will let you avoid these types of limitations.

Vista now has a new audio mixer that according to Amir works much better than Windows XP's Kmixer. Kmixer resampled all audio to 48KHz, unless the sample rate was already 48KHz. Audio originally from a CD source, which uses a sample rate of 44.1KHz, was always resampled to 48KHz and the method used by Kmixer degraded the sound quality. With the new mixer, maybe the algorithms for resampling are much better so the sound quality remains high. The new mixer also has a user mode audio engine where a user can set the default sample rate and includes an exclusive mode which provides access directly to the soundcard. With the user mode, the mixer will not apply resampling at all. However, its not clear if the mixer will just leave the source material alone so that if you are playing ripped CDs it will use 44.1KHz and when playing from a DVD, it will automatically switch to the native 48KHz.

Be sure to read Amir's posts in the thread linked above to learn about all of the other great audio processing features. Also, take a look at this post in the Windows Vista Team Blog about the new audio features in more detail. And here's an interview with Microsoft PM Hakon Strande who also talks about high definition audio in Windows Vista.

These features will only work if you send either a 2-channel PCM stream over S/PDIF to your A/V receiver, or analog signals directly to your receiver/amps. So for anything more than 2-channel stereo, including 2.1 (stereo plus subwoofer), you will need to use analog outputs. This might be a problem because most people prefer using their A/V receiver's processor and DACs especially when they perform better than the DACs included with inexpensive soundcards or the built-in audio chips on the motherboard. They also feel anytime an audio signal is present inside a computer, the signal will pick up noise generated by other internal components like the computer's power supply or hard drives, thus decreasing the sound quality even further.

However, using one of our future products, you'll be able to take full advantage of Vista's advanced audio capabilities and enjoy excellent sound quality because we use the same components found in high end dedicated DACs and the best pro soundcards. Since these DACs are located in our box, you don't have to worry about any possible noise generated inside the computer. In addition, our amp modules are very efficient, have lots of power, generate less heat and sound better than most amps inside your typical A/V receiver.