Creating a better DAC

Discussion in 'Interviews and Factory Tours' started by BarryT, Mar 19, 2021.

  1. BarryT

    BarryT MOT: Austin Audio Works

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    Hello, this thread will be about creating a better DAC from the ground up.

    I have been working on a DAC for my product line for a couple of years, searching the literature and listening to opinions. All this had to fit in with my getting to market my current two new products and the forming of my bootstrap startup company.

    I am Barry Thornton, my company is Austin AudioWorks, My BlackAMP is currently on tour with the SBAF comradery doing headphone amplifiers on the Loaner Program. AAW Black Amp impressions thread | Super Best Audio Friends You can read my past on my website . https://austinaudioworks.com/about-us/ or LinkeIn.http://www.linkedin.com/in/barrythornton. So much for all that, let's get to the interesting part.

    In a conversation with Sina of SBAF I mentioned that I am down the road with a DAC design and implementation, I could maybe in 4 months give him a GEM to tour through SBAF. He suggested that I do a "tell it all' about the project as a thread. From my perspective this is a great idea because as an inventor (34 patients) I know that I am subject to the 'Every Mother's Baby Is Beautiful' syndrome. What I make is great, that's the effect of Ego. Ego has no place in design work.

    Every comment that you make will force me to drive more articulately to the truth. You offer the reality checks I need to do this. So I will explain the decisions I have to make and the what and why that drives those thoughts.

    If you are OK with this then please join me and we both will learn things.

    My first comment is the next entry and I want to start by dealing with the raison d'existence of this thread, the What, Why, and of the DAC.

    Thank you
     
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  2. Armaegis

    Armaegis Friend

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    We really salivate over the guts of things here. Not just on measurements, but tell us what particularly challenges you faced and how you solved them. Any particular novel approaches that you had to use. Why did you select the dac chip that you did. Your approach to power supplies and analog stages, etc etc.
     
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  3. BarryT

    BarryT MOT: Austin Audio Works

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    I regret to inform you that your forum system will not let me post images. I have worked with Sina for last few days to no avail and without images explaining things it too text time consuming. I will put a hold on this for now until the forum sees fit to let me put images on.
     
  4. loadexfa

    loadexfa Friend

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    If you're OK doing a Zoom (or similar) call screen sharing can be really helpful for troubleshooting because the other person can see what is on your screen. I'd be willing to schedule something to see if I can help, PM me if you're interested.
     
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  5. insidious meme

    insidious meme Ambivalent Kumquat

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    Hi Barry. How are you doing this? The only way I can think of is to upload your images to a image posting website (I personally use Imgur) and then use the image icon on the insert ribbon above to individually enter a url of the image in your post.
     
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  6. rlow

    rlow A happy woofer

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    Would having a mod/admin change Barry to a MOT status give him image upload privileges?
     
  7. BarryT

    BarryT MOT: Austin Audio Works

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    I have loaded the images to Imgur but the forum system will not take the images but only lets me give you the URL meaning the my commentary and the image will not appear at the same time in the same place. The whole process becomes to arduous, hostile, and massively time (something I don't have a lot of) consuming. I will try to find a way. One gentleman offered to republish my stuff on the forum, a valid and viable solution but not one I prefer a this time. I will send him the AMP images but the DAC is deeper and more personal dialog and I would like keep everything in context. Thank you, we will find a way to get the system to work as it should. After all, this software stuff is supposed to be helping us, not hindering our expression of ideas.
     
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  8. BarryT

    BarryT MOT: Austin Audio Works

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    Thank you, I am still figuring out PMs (I am bit old-school at this).
     
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  9. Metro

    Metro Friend

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    The forum will take images from Imgur, but you need to use the correct link. Select your image in Imgur, then use the "Direct Link". Hopefully though, a moderator will give you upload privileges (usually reserved for Friends) which would make things much easier.

    Screen Shot 2021-03-21 at 12.39.34 PM.png
     
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  10. BarryT

    BarryT MOT: Austin Audio Works

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    Thank you, I just got of a zoom meeting with Sina and worked it out, I have been added to the right list and it all works normal now.
     
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  11. BarryT

    BarryT MOT: Austin Audio Works

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    We have to start somewhere so let's be pragmatists and start at the beginning.

    I am going to define a DAC for our purposes as a powered box with a USB input connection and a pair of balanced and unbalanced outputs (2 each RCAs and three XLRs (a pair of 3-pin and a single 4-pin).

    It should communicate with the user so we need to show that it is working (on),, that it is inhaling useful USB data, and perhaps how fast it is working (sample rate). Following the KISS (Keep It Simple Stupid) mantra, I would start with a blue power up LED, and sting of small LEDs in a row with data rates by them.

    I think it would be courteous of us to include an output level control so that it can directly drive an amplifier without an input control. That XLR-4 on the back will take both balanced outputs directly to one of my amplifiers (The Black AMP (headphones) or the Concept AMP (100 watts)) in a single cable.

    As for output signal level indication for the user, let's back probably the most important data, that would be headroom in this case. Power level doesn't matter, running out of power totally matters. I would suggest we consider either 1) get the world's coolest looking metering device that ever existed (I don't know that is) , or 2) some LEDs, they are off until the signal level is about -60 dB then turns green that varies with the level until we hit -9 dB and we go to go yellow, then at -6 dB go to red, or 3) nothing. I'm good for anything ,but what do you think?

    So we have a powered box with lights, knobs, connectors - what's under the hood?

    Basically we have four technology task areas to consider.

    1 - Take in USB data and arrange it into what is called I2C, or I squared C or Inter-Integrated Circuit bus protocol. It is a two conductor data bus or stream. One conductor is a clock, a repeating pulse that times everything, it's kind of like a drummer in a band, it keeps the beat so it all makes sense. The other conductor is the data. a sequence in packets (words). To make this work for audio a third conductor was added to the 'frame' the data to indicate whether it is Left or Right channel data. It would look like this if you could see the energy flow.

    [​IMG]

    Therein is the sum total of the audio information in digital form. Timing and information. More about this later.

    2 - The interface that converts the streaming pattern of the digital data bits into a streaming digitized power packets of micro-Watt size

    3 - The interface that turns the streaming digitized power packets into a varying voltage.

    4 - The analog post-processor that absolves all the digitized packets of their digital sins upon the analog signal.

    So we have four subjects to master to make our box reproduce eargasms.

    Up for it?

    Next time I aim my keyboard this way we will look at issue #1. But for now let me bring you up to date.

    I looked at the flow described above and built a quick and easy prototype giving me a working physical platform upon which to execute my 'first pass" conceptualization. I used as much OTS (Off The Shelf) hardware as I could. I built what I couldn't buy.
    [​IMG]

    [​IMG]

    I put it out to a group of local 'ears' who have been with me for the entire journey. Very positive remarks from digitally critical listeners. I was going to put the finished version of this into the market.

    But it didn't feel right. I knew in my gut that I was on the verge of putting the pieces together in a different and better way. I shut the DAC project down in November, let people listen to the unit, got 'feel goods' but philosophically had issues with the solution set I chose.

    After the Holidays the ducks started lining up in a row. I read a book years ago that affected me to a good degree, it's by a guy named Douglas Hofstadter and it is called 'Gödel, Escher, Bach: an Eternal Golden Braid'. Brilliant stuff, but to the point. He proposes that your mind is like a maelstrom, a chaotic whirlpool of thoughts. You, the cognitive you, the homunculus I say with a smile, looks into the cacophony of mental images, once in a while all the crap lines up enough that for just a split second, a pattern is revealed. Then it's gone - but you remember. It is an idea.

    I had an idea, and where we go from here is the manifestation of that vision.
    So next we look at Part #1, the digital process, and the prototype. We resolve the good, bad, and ugly of it.
     
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    Last edited: Mar 21, 2021
  12. Erroneous

    Erroneous Friend

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    It's so cool to get the seemingly inside view of the birth of something like this. I'm guessing it must sound good based on the mad scientist vibe I get from this dude. And it's not like he plans to release a line of DACs. Just one DAC. No pressure. ;)
     
  13. loadexfa

    loadexfa Friend

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    It's very interesting to get a look into your process.

    For this crowd I would encourage an additional input such as AES, I2S, and/or SPDIF. USB is notoriously "dirty" and a number of us are using a Pi2AES or similar for a cleaner input. I understand this is early in the process, I would assume it's cheaper to plan for something like this earlier rather than later.
     
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  14. purr1n

    purr1n Finding his inner redneck

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    Try now.
     
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  15. BarryT

    BarryT MOT: Austin Audio Works

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    Yes, you are right and I forgot the other variants of digi-audio, it's just connectors and code as we will see in the post about Task #1
     
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    Last edited: Mar 22, 2021
  16. purr1n

    purr1n Finding his inner redneck

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    One of these days, I will need to make a trip up to Austin so check out what you are cooking up. (Will sign NDA of course - actually if you meet any of the forum members, we are really good at keeping secrets).
     
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  17. pavi

    pavi Almost "Made"

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    this is wonderful! thank you, @BarryT, for inviting us into your design process.
     
  18. BarryT

    BarryT MOT: Austin Audio Works

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    Hello, back for Part 2 of this discourse.

    I would like to start with a remark. Design is about change. You don't design something that already exists, you design something that doesn't exist and thus is new. Things exist in our minds that are barriers to change, our beliefs and our personal convictions are almost always based on the myths we subscribe to. Myths, sometimes they expand our horizons, other times they limit them.

    I say this to remind you that audio is illusion and myth for the whole being, not just your aural sensations.

    I also want to point out that we are all essentially the same critters, my mind is like yours and yours is like mine. You know how I feel and I know how you feel. We speak the same language and we think in common words. We chose different paths to get the 'software' we run under but the basic machine is the same.

    As I grow intellectually I have many times had to understand that what I thought I knew was wrong. Then I had to take a new path, learn a new vocabulary, and take new risks. We all will change.

    Here is a visual of what I outlined in the first part of this story.

    Flow.jpg

    Make each step right in this flow and you should get a great sound. So let's see if we can do just that.

    Nothing in DAC electronics has more mythology attached to it than the gadget that inhales USB and exhales I2C. Step #1 in our sequence. Taking what could be a chaotic digital data stream of packets and making them into a very well regimented digital stream of bits can be a bitch. Turns out to be about time and timing constraints, but nothing magical. Most folks tend to focus on one digital flaw, that of 'jiffer'. It's kind of like THD in amplifiers or horsepower in cars, a symbol of something that is supposed to tell you how it will feel in your head. I am suspicious of simple issues in audio, I always know that the Marketing Department is hard at work.

    In the beginning we had lots of issues with making all the parts do the right jobs. The USB audio signals were sometimes erratic. But very rapidly the guys designing both ends of the USB audio chain began to talk to each other. Digital audio became a big deal for home theater and the whole entertainment supply chain. Money poured in, things got done, and all the stuff started to work rather well. Specialized hardware helped a lot. ASICs and RISC chips made the scene. Then some computer chip companies decided the market was big enough to do it a better way so we advanced to audio in software.

    To build my prototype I bought a single board DAC from China. It worked as you would expect a single board Chinese unit to act - it meets specs but "sounds like hammered feces", a quote an old friend of the 70s Berkeley CA audio scene (he imported koetsu and owned SOTA, was an outspoken audio participant). He once revealed to me that the sound he was describing was 'splat', and that is what it sounded like. Everything went spat. I am sorry to say he died last month, a loss to the audio community.

    The board you see in my proto-platform does Step #1 of our task list is using a USB hub and a USB-to-I2C converter. It is totally dependent on the incoming USB signal for timing. It is a design that could be made from cheap OTS (Off The Shelf) parts and there was no licence fee. It works OK because the guys who wrote the send end in my laptop had done a good job on the Audio USB Driver. My hat's off to them. If the USB timing is off just a bit then this board is screwed. So is the audio output.

    A couple of years ago I picked up a small board with a dedicated XMOS chip and all the licenced software in a field programmable memory. I can update as the software gets better, there is a big community of developers, and works flawlessly. I get great I2C out of it all the time. It also takes in SPDIF and with some tinkering AES/EBU. Here is a picture of the development board.

    DSCF0428.JPG

    So where we are is that I don't have to reinvent the wheel and I don't have to get a licence for software which, by the way, that comes with a community of support. And there are multiple vendors of his, could use an Arduino or pi supported with open source code. Everybody winds up copying everyone else, or improving one their patents and IP. Like all technology that has been in use for a while, the working praxis implementations become typical or SOP.

    But today I can make it work and build with this card expecting to get the results I am looking for.

    So much for the easy part of this DAC and fortunately for us the 'sound' of digital does not reside in the digital side of the equation. Unless it screws up Step # 1 it is transparent to the process of making analog audio. We will tackle a sonicly more relevant issue next, that of making steps of analog power.
    --
    Barry Thornton
     
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    Last edited: Mar 27, 2021
  19. BarryT

    BarryT MOT: Austin Audio Works

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    Part #3 - Digital bits converted into quantizd chunks of electrical power.

    The digital audio data we want to listen to is typically made up of two (16 bit) or three ( 24 bit) bytes of digital data in a time based sequence. While many combinations are possible, for the sake of this discussion I will choose a word made up of three bytes (24 bits) that is sampled 96,000 times a second. Rather than drag you through a keyhole explaining the various schema available to make a DAC work I will refer you to Wikipedia for a good summary at https://en.wikipedia.org/wiki/Digital-to-analog_converter

    We basically have two ways to do this. We can chop the data up further and bit-by-bit stream it out (delta-sigma bit-stream), or take entire words and convert them at one time (multi-bit). Are there other ways? Wellllll yes, but not too inviting, what I would call 'corner cases' and expensive.

    Funny thing is it is one or a bunch of switches, but in both cases, it centers around a switch. The key to this conundrum is the switch.

    Searching the literature and talking to folks of a couple of years, listening to different products and more searching the literature both academic, professional, and anecdotal leaves me in the same place as most people and that is trying to sort out the myths in the mythological world of digital audio.

    I will remark that by far and away I feel that the most seductive way to do this is discrete R2R with big honking switches. Personally this appeals to me a lot, it is more 'organic', a bit of the 'man-against-machine' and the like. To me I guess it's counter culture appeal is very seductive. Reports on it are mostly positive and passionate - and are more myths.

    Such is what I would like to believe.

    So what do I know?

    Years ago I was the VP of a company called Opto-Digital Design (owned by Monster Cable). Digital through fiber-optic cable. We did snakes digital audio and video for performing sound and. Big in snakes (the cable that connects all the stage microphones to the mixing suite and recording truck at a concert). A big cable, typically over 50 microphones going a couple of hundred yards or more, the bane of live performance, weighs hundreds of pounds, hard to move and secure, and every time you unroll it and the roll it back up again you wind up with a broken leads so you need lots of spares in the cable.

    Our products replaced the snake with a single fiber cable. It were used in touring concerts and big venues, our big customers were organizations like DisneyLand, Bulls Stadium, Alamo Dome, Dollywood, major studios and network, ESPN, etc. For 4 years I developed digital audio , 24 bit, 48 and 96 kSample, for a very critical market of professional mixing engineers and performance artist doing live recorded sound. I had a budget to research and test analog, digital chips and processes, I'm big on prototypes and doing field testing. I learned and that knowledge sat dormant for two decades while I went to inventing computer stuff, doing corporate business, and getting patents. Then I began to remember.

    Perhaps the most important thing. That prototype I showed you in the first installment of this thread. It was my first reaction to making a DAC sound better, it worked, and sometimes first passes are the right idea, you just have to relearn enough for the science to catch up with feeling.

    Maybe I was right the first time. I now think so. As we shall see, it was solving the switch problem.
     
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  20. haywood

    haywood Friend

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    Very interesting series of posts, I’m looking forward to seeing where this is going.
     
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