Tag Archives: DoP

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina Audio and Home Theater specialists present Cane Creek Audio and Paul McGowan of PS Audio, Intl.

This was a good one for me, as a good explantion of DoP by Paul and this makes sense.


The three-letter acronym, DoP has a number of meanings depending on what you’re interested in.

To the Italians, D.O.P. stands for Denominazione di Origine Protetta (Protected Designation of Origin): the name used to indicate a product that owes its characteristics to its place of origin, and its production, modification and processing occur within that geographical area. Bubbly Champagne from Champagne France, and tasty Moderna vinegar from Moderna Italy.

For Audiophiles, DoP stands for DSD over PCM. Playback Design’s chief digital guru, Andreas Koch, invented DoP as a means to allow DSD to be compatible with computers not possessing the means to deal with it.

A good (short) video on the subject is one our own Gus Skinas and I put together in my older series called Lunch with Paul.

DoP has a marketing problem. The mention of it has many purists running for the hills. Why? Because it is assumed DoP converts DSD to PCM, thus changing forever the characteristics of DSD we all love.

Two things are wrong with this. First, DSD is not being converted to PCM. Second, even if it were, there’s no sonic penalty when done correctly (though in their defense it rarely is).

Today’s computers don’t know what to make of DSD. Without a special driver and program installed, a Windows or Mac computer sees DSD as unrecognizable noise. This is because DSD is very much like analog: a continuous unbroken stream of moving data that can be directly listened to as music. PCM, on the other hand, is made of discrete chunks of data each with its own ID that serves as a routing map.

What Andreas did was really clever and simple. Instead of trying to fit a square peg (DSD) in a round hole (the computer), he simply broke the continuous DSD stream up into discrete chunks and added an identifier bit that serves as a routing map. To the computer, DoP looks like PCM and it merrily passes it along to your DAC.

When your DAC gets this “PCM-like” stream of data, it knows to remove those added identifier bits and reassemble the unmolested virgin DSD bits back together so we get that analog-like continuous data stream called music.

The DSD data is identical to its beginning. It was never converted to another form.

Hope that helps.


Asheville’s Home Theater and Audio specialist presents Cane Creek AV and Paul McGowan – PS Audio, Intl.

Why is it never easy?

How many times have you tackled what would seem to be an easy project, only to find it’s anything but that?  Best laid plans and all.

Because I travel to shows and clubs demonstrating our products, in particular DirectStream as of late, I just carry a bunch of discs with me, hoping the venue has an adequate player to connect up with.  Inevitably this means only CDs, as there are very few disc spinners that output DSD or convert to DoP on the fly.  What one needs is a computer.

So over the weekend I decided to fix that problem and build a small music server from a Mac Mini.  This ultra quiet, tiny computer is a mere $599 out the door, has plenty of storage for what I want and can be operated without a router and controlled from nothing more than an iPad or my phone.  Sounds perfect.

So on Sunday off to the Apple store I went, purchased the device and figured I’d have it up and running in a matter of hours.  So simple would this project be that I would then start a series of daily posts describing to you step-by-step how to make your own so you too can share in the fun.  It really is a perfect situation if you are planning on having only one DAC and storage setup.  If you wanted a network solution, then of course the Network Bridge would be the obvious choice.  But traveling I don’t need a network, I don’t need to connect to the internet, heck, all I need is a good USB cable, DirectStream and this box.

Were it only so simple.  Well, stubborn as I am, it’s going to be simple and hopefully the pain I am currently suffering to get this working will be to your benefit when I share with you the easy steps to make it work.

Wish me luck.

Asheville’s Home Theater and Audio specialist presents Cane Creek AV and Paul McGowan – PS Audio, Intl.

Back to the classroom

Thanks for indulging me my story of the early struggles with an outdated education system.  I hope we’ve come a long way since those days of industrialized factory schools churning out something; although I am not sure what.

The saving grace of my education through public schools was the few standout teachers I had (and I suspect you had as well).  Hats off to those brave souls that really loved to teach and share and gave their all towards that endeavor, despite an antiquated school system that hadn’t changed much since it started, back in the Henry Ford days.

Let’s finish up with DoP and move on to other subjects.  If you’ll recall, DoP is a format that permits single bit audio (DSD) to “trick” a computer or network into thinking its Multi-bit Audio (PCM).  Because computers don’t recognize Single-bit Audio, they don’t know what to do with it.  And that brings me back to what I asked you to memorize: that Bits are Bits.  To a computer a video bit, math bit, audio bit, or mouse bit all look the same.  Bits is bits.  Remember?

Now, don’t get turned around just yet.  Many of you wrote in to say “if bits are bits, why do cables matter, sample rates, etc.?”  Ok, that means you’re thinking too much!  I’ll likely call Mr. Shannon out of retirement to give you a good whack for doing so.  🙂  When I write “bits are bits” I am not referring to how those bits are delivered, their speed, their timing and all the little details critical to how those bits are going to sound.  No, I am referring to the bits themselves: the ON and OFF pulses are all pretty much the same.

So if bits are bits, how do Single-bits differ from Multi-bits and how does a computer know the difference?  Computers use something called a header, which is a small group of bits that represent an instruction set.  The header always comes first and tells the computer “I have PCM or I have DSD or I am USB” and with these instructions, the computer (or DAC) knows what to expect next and what to do about it.

The problem we run into with Single-bit Audio is two fold: it’s a stream and doesn’t have a consistent “reminder” header telling the computer what’s going on and most modern computers were never instructed to deal with Single-bit Audio even if they did have the instruction set.  They only know Multi-bit Audio.  Think of this as getting a set of written instructions in a language you can’t understand.  That could change, over time if operating systems of Microsoft and Apple wanted to include Single-bit audio, but for now they don’t.

So here’s what some clever guys did to get around this problem: they put sheep’s clothing on the pack of wolves.  If you had a flock of sheep and wanted to get a pack of wolves into that group without the sheep noticing, you’d wrap the wolves in sheepskin so the sheep would be fooled.  Now let’s relate that to Single-bit Audio (the wolf) and Multi-bit Audio (the sheep).

Single-bit Audio is a stream of on/off bits.  The more ON bits the more energy we generate to make a loudspeaker move.  Multi-bit Audio is not a constant stream, but rather a stream of coded packets (their bits also make more or less energy to the loudspeaker, but they must first be decoded, unlike the simpler Single-bit stream).  Think of Single-bit Audio as a flowing stream of water and Multi-bit Audio as a long unbroken freight train.  Each of the cars in our imaginary freight train has an identifying marker that lets an inspector know what’s inside each of the cars of the train.  This is the header I spoke of.

If we want to take our continuous stream (Single-bit Audio) to a new location, one thing we could do is divert a section of the stream’s water and fill up one of the freight train cars.  If we repeated this process, using all the freight train cars, we could transport an entire stream intact to anywhere we wanted.  How did we manage this?

Picture our stream running in an overhead pipe with a gate on the pipe that opens up at identical intervals, releasing water.  Below the pipe is our train.  With each water release we fill up one of the cars of the train; the train then moves forward and the process repeats.  Using this method, the train can travel anywhere it needs to go.  What we’ve done is expertly divided up the water in the stream into containers (the train cars) which allows us to transport the water intact to a new destination.  Once we arrive all we need to do is reverse the process and we again have a flowing stream.  The water is identical, it’s in the same order it started with and it was never converted to something else for transport.

Now you start to understand how DoP does not convert Single-bit Audio to Multi-bit Audio, it simply breaks the continuous stream of bits in Single-bit Audio into identical groups, wraps an additional piece of info around it and fools the computer into thinking it’s actually something it is not.  The computer’s happy, the data is intact.

Remember that the bits are bits and the computer can’t tell one bit from another?  Once we add this header that is lying to the computer, falsely identifying the attached group of bits as PCM, the computer lets them through because it simply cannot tell the difference and doesn’t care (they pass through unmolested but the computer still doesn’t know what to do with the DSD bits and thus can’t play them without a program to help it understand them).

For the more technically minded here’s the details.  The Single-bit Audio stream is running at 2.822mHz (2,822,000 bits per second).  The DoP “converter” simply culls out 16 bits from the Single-bit stream and attaches an 8 bit header to it, then repeats that process over and over again.  The bits it is grabbing have no timing information associated with them; they are simply a group of exact ON/OFF bits in the exact order they started with.  16 audio bits, plus 8 header (information) bits equals 24 bits.  So a DoP packet is 24 bits long (8 info bits and 16 data bits).  Each of these newly minted packets collectively run at 176.4kHz.  Sound familiar?  Sure, you’ve heard of high resolution audio running at 176.4/24 bits?  Right.  That’s single rate DSD in DoP clothing.  You can do the math yourself: 16 x 176,400 equals 2,822,400 which is the exact sample rate of single rate DSD.  Simple eh?  And the other added 8 bits?  They account for the larger file size of DoP vs. native DSD (bigger by 1/3).

Here’s a picture of what that looks like.


The orange squares to the left represent the 8 information bits attached to the 16 bits of DSD to the right.  This is our freight car filled with Single-bit water (the wolf we’re trying to hide), and the 8 header bits provide the sheep’s clothing to trick the computer into believing the next set of bits are PCM, not DSD.

Lastly, one of the 8 information bits lets any interested party know the data is really DSD.  Thus, if the DoP data is put into a DAC that understands that information and can process it, all it needs to do is throw away the 8 bits of information data, connect all the 16 bit wide groups of DSD together and play the DSD stream perfectly.  No conversion process ever took place.

Now, let me go grab a cold glass of perfect water from the stream, uncontaminated from any dreadful impurities, despite the fact it arrived in a freight train with a wolf as engineer.

Asheville’s Home Theater and Audio specialist presents Cane Creek AV and Paul McGowan – PS Audio, Intl.

Cramming useless information

Nothing upset me more about school than being asked to cram useless unrelated information in my head.  Later in today’s post I will ask you to do just that.  If you fail, I will come after you with a ruler across the knuckles.

We’re in the middle of a set of posts helping us understand what DoP is.  DoP is DSD over PCM which, if you don’t understand what those Three Letter Acronyms stand for, makes no sense whatsoever.  To help wade through this mess I’ve replaced the acronym for the CD standard, PCM, with another term: Multi-bit Audio.  I’ve then replaced the SACD standard, DSD, with a second term, Single-bit Audio.

Using these easier terms, DoP is a means to send Single-bit Audio to a computer using the language of Multi-bit Audio.  And here’s the thing to take away from this understanding: when using DoP, Single-bit Audio is NOT converted to Multi-bit Audio.  That’s a popular misconception that we’re working on getting straightened out.  There is no conversion of Single-bit to Multi-bit when we use DoP.  Single-bit stays as Single-bit.

Before we get into the nuts and bolts of it I would ask you to put one fact inside your head (my ruler is itching to rap someone’s knuckles).  Put it in there, let it rattle around, even if it doesn’t make sense, and hopefully it’ll stick somewhere in the deep caverns for later use.  Yes, there’s a test later.  I know, it’s the same terrible request your teachers made of you in school.  ”Just stuff this fact in your head, despite the fact it makes no sense.”  Terrible way to teach someone.  The worst.  But it did give them the excuse to whack a few students around.

Inside a computer, bits are bits.  The bits of Single-bit Audio are the same as the bits in Multi-bit Audio.  Bits is bits.  Got it?  I promise, it’s all I will ask you to store.  Onward.

What does DSD look like?  How does it work?  It’s actually simple.  It is a system that uses bits to generate energy.  The greater the energy generated the higher the signal level; the lower the energy, the lower the signal level.  Have you ever seen a wind turbine that generates electricity, or a solar cell doing the same?  The stronger the wind, the brighter the light, the more energy generated.  In the case of DSD, more ON bits means more energy.  Fewer OFF bits, less energy.  Take a look at the following picture.


The blue rectangles represent ON bits and the white rectangles represent OFF bits (click the picture to expand it).  The red line is the resulting music in the form of a sine wave.  See how the red sine wave is going up whenever there’s a bunch of blue rectangles, and down when there’s lots of blank ones?  That’s it.  That’s all you need to know to understand Single-bit Audio (DSD).

Remember there are only two kinds of bits: ON and OFF.  An ON bit simply means there’s voltage present – just like you had connected a battery between the plus and minus terminals of your loudspeaker.  An OFF bit has no voltage present, it’s just an empty space, as if you removed the battery from your your loudspeaker.  Connect a battery across your loudspeaker and the driver will jump forward and move the air.  Remove the battery and the loudspeaker driver returns to its resting position.

If you were able to connect and disconnect your battery from the loudspeaker 2.8 million times a second, you’d probably get a free Guinness beer and a place in the record book of the same name.  But if you could ….. then you could duplicate what’s in the picture and sound would come out.  Music would be there if you followed the right pattern to match the music.

And that’s Single-bit Audio.  Now, don’t forget what I asked you to cram into your addled brain.  You’re going to need that important piece of useless information tomorrow.  Now, where’s that ruler of mine ……

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Yesterday’s post as well as a few earlier ones

Wading into it
DoP isn’t PCM
We are all reviewers
Beware of perfectionists
The truth of the matter

Asheville’s Home Theater and Audio specialist presents Cane Creek AV and Paul McGowan – PS Audio, Intl.

DoP isn’t PCM

Ok, there’s just too many TLAs going around here (Three Letter Acronyms).  Engineers are obsessed with them because it makes for quicker communication of complex terms, and that makes sense, but what’s a poor Audiophile to do?

Recently I have been getting a lot of email questions about DoP (DSD over PCM) and most of the questions would suggest folks aren’t understanding what DoP is.  In fact, much of the mail I have been getting suggests folks think DoP is converting DSD to PCM (there’s those pesky TLAs again).  And the question that generally come from that partial misunderstanding is “I don’t want to convert pure DSD to PCM, it’ll change the way it sounds”.  Right.  Wrong.

Right that converting DSD to PCM changes the sound; and there’s a group of folks that find DSD downsampled to PCM sounds better than DSD (as illogical as that sounds).  I have personally heard examples of this “betterment” and while I too hear the improvements, I remain unconvinced this is anything but an anomaly we need to figure out.  And then there’s DirectStream that converts PCM to DSD and definitely sounds better for it.  It’s all so confusing.

Wrong that DoP has been converted to PCM and that it will sound different than DSD; it isn’t and doesn’t.

Tomorrow, let’s take our time and get to know DoP a little better and gain an understanding of how it works and what’s going on.

See you tomorrow.

Sneaking in the back door

With the growing interest in DSD, which is the main format of SACD, I thought it might be helpful to explain DoP.  Yeah, I know, too many TLA’s! (Three Letter Acronyms).  DoP stands for DSD over PCM and was invented by a group of high end audio manufacturers doing their best to get great sound to all the rest of us.  PCM is the standard format for digital audio like that found in CD’s.

So here’s the idea.  Because the PCM format is everywhere, a format understood by all digital audio players, computers and DACS, it is the logical candidate for a format.  As you can imagine, getting all the computer manufacturers and operating system manufacturers together on something as little used as DSD would be a huge undertaking and one that probably would never get off the ground.  But if it were possible to leverage an existing format, like PCM, then it’d be a much easier task.  And that’s just what these folks did.

The PCM format uses a series of frames, or snapshots, for the data.  Each frame is a separate grouping of audio containing a left and right sample.  In a CD we get samples of the music and each sample is taken 44,000 times per second, once for the left channel and again for the right channel (so the process happens twice as fast in order to get two 44K samples in the same time).  Now, mentally take those two samples (left and right) and put them into a package.  That’s the frame we are talking about in PCM.  Each frame contains one left and one right sample along with some extra information that explains to the equipment what to expect.

The DSD format, on the other hand, does not have any frames; instead it is a steady stream of bits with more or less density according the the music.

So here’s the clever thing the designers of DoP did.  They simply took the DSD stream apart into discrete 16 bit groups; every 16 bit block was separated from the stream.  They then combined a 16 bit right group together with a 16 bit left group, added the identifier information and dressed it up so computers and DACS would think it’s PCM.  As far as any computers or USB streams are concerned, it is indistinguishable from PCM so it is passed onto the DAC via USB, S/PDIF or AES/EBU.  Very clever indeed.

To match the speed of single and double DSD, they use 176.4kHz and 352.8kHz PCM rates respectively.

Once it gets to the DAC, it is then converted back to its original stream by simply connecting all the bits back together.  There’s no data manipulation, the bits are unscathed and, if your DAC can play DSD you’re good to go.  If the DAC does not support DSD, you get silence.

Paul McGowan – PS Audio, Intl.