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Driving the music

Paul's Posts — 10 September 2012

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Driving the music

When we think of streaming audio we probably gloss over all that’s involved – and there’s a lot involved.  You’d think streaming audio should be as easy as selecting what you want to hear, pressing a button and getting it to play.  In some cases it’s that easy, such as using Apple’s Airplay option, but with every easy solution comes a host of restrictions and limitations you have to deal with.

Today I thought we might explore the most basic streaming audio option: streaming to a sound card inside a computer and playing the audio to your DAC.  Later we’ll take a look at the same thing only connecting over your network.  The first thing we need to understand is how your computer communicates with your DAC.

The vast majority of streaming audio use in high-end audio is when you’re tethered to your computer through USB or TOSLINK.  In this popular setup, the DAC is the player and is connected to the computer either via USB or through a digital output if one is included with the computer.  Like a dog and its owner out for a walk, the pair are forever tied together on a short leash unable to operate independently of each other.

Since the USB connection is the most popular “short leash” solution (USB Is limited to something less than 3 meters) I will keep the discussion centered on USB.

The first thing we should understand is the need for a driver to make this work.  So, what’s a driver?  A driver is a small piece of software your computer uses to communicate with another piece of equipment.  Because your computer is asked to connect and control or be controlled by attached equipment like printers, speakers, video monitors, your mouse, your keyboard, etc. a method had to be devised that helps the computer understand what it is being asked to do with connected peripheral equipment.  Every attached piece of equipment you use has a driver the computer uses to connect up to it – and your DAC is no different in that respect than your printer or keyboard – you just have to make sure the correct driver is installed.

From a user’s perspective it may not seem like you need a driver for something to work – like when you plug in a printer, USB memory stick or keyboard and it just works.  But this is only an illusion – as everything you add needs a driver.  So when you plug in your printer and it just works, what actually happens is the driver for this device was already installed on your computer.  Macs make it really easy for people to connect gear – not because they are better machines – but because Apple constantly adds new drivers into the computer’s memory so it just seems effortless when you attach a new printer – and from the user’s perspective it is seamless and easy, but it takes a lot of work on Apple’s part to make that happen.  In other words, there’s no magic going on at all.

Ever notice that most modern DACS are limited to 24 bit 96kHz on their USB inputs while the DAC itself is capable of higher sample rates? The reason for this is that both Mac and Windows computers have preloaded drivers that support this level of USB audio and USB chip makers provide plenty of easy-to-implement solutions based on these drivers, making it super easy for users to simply plug in the device and DAC manufacturers to implement it on their DACS.  Plug-and-play still requires drivers to be installed, but in this case the drivers were loaded without you, the user doing anything.

When you connect up our new PS Audio Mark II DAC that offers 192kHz 24 bit USB performance, it “automatically” connects on a Mac computer yet Windows computers require you to download a driver and install it to make it work.  Again, Macs simply have the needed driver preloaded and Windows doesn’t – but it won’t be too long before they will.

The whole point is not to make a comment between Mac and Windows but to help you understand what a driver is and what it does.

So, in conclusion, whenever you attach and connect anything to your computer, from a mouse to a DAC, the proper interface or driver must be installed to make it work.  The driver merely tells the computer what your attached device can and will do and how to communicate with it.

Tomorrow we will discuss getting music to the driver and what it means.

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About Author

Paul McGowan

Paul McGowan is the CEO and co-founder of PS Audio Inc. a Boulder Colorado design and manufacturing company of high-end audio products and services. McGowan has been designing and building high-end products for nearly 40 years. Hobbies include skiing, music, hiking, artisan bread baking, kick boxing and cooking. He lives in Boulder Colorado with his wife Terri and his 4 sons.

(5) Readers Comments

  1. Soundminded

    September 10, 2012 at 5:45 am

    Here’s the distillation of an entire course on information theory in a few sentences.

    Information in the form of an electrical signal can be thought of as passing through a channel. An information channel consists of two dimensions, amplitude and time. Time can be equally be thought of as frequency so sometimes it is convenient to think of the dimensions of the channel as amplitude and frequency instead.

    There are two important elements in each dimension, range and resolution. Range is the difference between the highest and lowest amplitude and highest and lowest and frequency. This is the siize of the rectangle that defines the limits of the channel. Resolution is the smallest incremental change from one amplitude level to the next, from one frequency to the next that is detectable.

    The requirement for an information channel’s range and resolution depends on the nature of the information in the electrical signal being processed, in this case the digital version of an electrical analog of music and the range and resolution of human hearing. Even though it is in digital form, it can be seen in analog terms because it will be an analog form before it passes through the channel and converted back afterwards.

    What is the characteristics of the RBCD standard and how does it stack up against the requirements for humans listening to music? What are the numbers?

    The dynamic range of human hearing is about 120 db at most at some frequencies. This is the difference between the threshold of hearing and the threshold of pain. At the frequency extremes the range is much lower. However the most dynamic music (not the loudest but the music with the greatest range is a symphony orchestra. The noise floor in an absolutely quiet concert hall is 27 db absolute (c weighted) which is the design criteria set by AIA (Architectural Institute of America.) The loudest sound it can make is 105 db. Therefore for convenience I’ll say the greatest dynamic range is 80 db. It was believed for a long time that the smallest increment humans could hear is 1 db. I think I can sometimes hear 1/2 db. A certain editor of a famous magazine claims 1/10 db (Personally I don’t believe him but let’s pretend he knows what he’s talking about for now.) That would require a channel capable of 800 levels of sound over a range of 80 db. RBCD I think uses 14 of its 16 bits for the word constituting amplitude. Since the number of levels is 2 to the X power in a binary system (ones and zeros which is what RBCD is) it will produce over 16,000 levels over about a 100 db or less range or more than 160 levels per db change which is 16 times the resolution claimed by that editor.

    What about time or frequency? In theory the greatest slewing rate would be from one extreme 0 to 80 or 80 to 0 in 1/2 cycle of the highest audible frequency or 80 db in 1/40,000 th second. RBCD can do it in 1/44,100 seconds so it is faster than the fasted slewing conceivable (no music contains such a rapid change unless you possibly stuck your head 1″ from crash cymbals smashed together as hard as they could be struck.)

    Two other criteria deserve mentioning. One is frequency stabilitiy. For a turntable or tape deck stability depends on the constancy of a motor, flywheel effect and belt or idler wheel slippage. 0.1% frequency wobble (wow and flutter) is very good. For RBCD the stability is that of a quartz oscillator measured in millionths of a percent. For all practical intents and purposes RBCD does not exhibit frequency drift.

    The other is amplitude linearity which would show up as harmonic and intermodulation distortion in the analog domain. There again RBCD hardware simply is in a different league from analog systems.

    So where was the problem in early players? Probably in the conversion from digital to the analog domain with those pesky low pass filters that rang creating spurious sounds in the audible range and random errors in reading bits. Those have been fixed with oversampling allowing extension of the filtering to frequencies far beyond the audible range where ringing is inaudible.

    Therefore RBCD when executed perfectly according to its standards exceeds the channel requirments for all music without compression or equalization. It doesn’t need any because unlike physically dependent channels which are subject to saturation of magnetic tape, excessive modulation of record grooves, excessive sideband modulation of FM broadcasts, and excessive background noise in all of them which limit their usable dynamic range, the digital system is merely expressed as numbers, one number being no different to the system than any other number. What’s more other digital systems are possible with any arbitrarily defined range and resolution. That they haven’t been developed to replace RBCD even at the insistance of high end audiophiles who work in the industry is because they aren’t needed. Once the information channel meets the required performance criteria, further improvement offers no benefit whatsoever.

    OK, now that you’ve had your course and passed your exam, you can send me your tuition money.

    • September 10, 2012 at 6:19 am

      Wow, thanks! As always, great information – not that I agree with you on all of this – but valuable for sure.

      • Soundminded

        September 10, 2012 at 10:52 am

        I’d be interested to know on which technical points we disagree.

        • September 11, 2012 at 6:54 am

          Mark, your technical analysis and discourse are wonderful – I too am learning from reading them. Sometimes your end result is so emphatic as to offer no room for what others perceive to be true.

          “That they haven’t been developed to replace RBCD even at the insistance of high end audiophiles who work in the industry is because they aren’t needed. Once the information channel meets the required performance criteria, further improvement offers no benefit whatsoever.”

          This is a logical assumption based on the info you presented and is well thought out – to be sure. Hard to refute based on the evidence presented. It reminds me of a really good attorney addressing a jury in his summation. “And so, here are all the facts presented in logical order and the conclusion, based on those facts is irrefutable, so you must convict the defendant.” Only, the defendant is really innocent (in this silly example) and the attorney left out some details that didn’t suit his case.

          I am not suggesting that what you wrote is wrong – it is not and it is irrefutable. I just don’t think it’s the whole story and I am convinced we don’t understand the whole story well enough to really offer a plausible explanation about why someone like Michael Fremer can consistently identify tiny changes that technically shouldn’t matter – or we can prove don’t matter.

          But keep it coming! I love it and am learning a lot from you.

  2. Soundminded

    September 15, 2012 at 6:48 am

    Thank you for your kind words. I am the product of the people who taught me, trained me, directed my education both theoretical and practical. I was extremely fortunate. They were some of the best people I ever knew. They were very knowledgeable in their fields, set very high standards, and were merciless when I got things wrong. I wish I knew even a tenth of what they knew. Perhaps of all their gifts the greatest were the ability to learn by teaching myself independently of further formal training when necessary and the facility to think critically, to question everything. (That doesn’t make me very popular in some places but I don’t care. The weight of popular opinion makes no impact on me if it flies in the face of what I’ve learned through training and experience.) If I make a mistake, an error in fact or logic, then so be it, I will accept that when it is shown to me. My views are open to change but evidence must be compelling. I’m not easily swayed. There are far larger scams than those in this industry. Beyond deliberate deceptions, even the best people with the best of intentions can make honest mistakes. I don’t think any the less of them for it but I don’t take anything as fact on blind faith alone and I don’t ever pretend false is true.

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