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Thread: Digital Audio for Dummies, like Me.

  1. #1
    Senior Member 1audiohack's Avatar
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    Digital Audio for Dummies, like Me.

    I am away from a PC and hate writing via phone so please excuse the brevity.

    I spotted this link on ProSoundWeb. It reminded me of a conversation I had with Prof Doug Jones (currently working with Danley Sound Labs) a year or so ago about digital signals and processing.

    Take a look and give it a think. I would love to discuss it more, but from a key board!

    https://www.youtube.com/watch?v=cIQ9IXSUzuM

    All the best,
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    I really like the guy's presentation, it's obvious he knows his material. He covered bit depth quite well, I'd love to hear his explanation of sample rate.

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    Thank you Barry!

    There is a lot of excellent ancillary stuff along with it.

    Ed
    Sawdust is my co-pilot

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Ed Kreamer View Post
    Thank you Barry!
    Ditto!

    There is a lot to digest there. I'll be listening to it again and follow up with his other postings. I do want to know more about the effects on transient response.

    I'll post again after more research.


    Widget

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    Senior Member Ducatista47's Avatar
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    Nice information and presentation. I guess I was familiar with his work because years ago I downloaded and printed out the paper he alluded to in the beginning. The link to it, and many other links as well, are in the web page for this video. https://wiki.xiph.org/Videos/Digital_Show_and_Tell

    The stair step explanation (of why the phenomenon does not even exist) would be embarrassing for all the audio writers who used them as the "proof" that digital audio could not possibly be capable of accuracy or real fidelity. The ignorance (note - not stupidity) of these arguments was obvious to me, but there is no reasoning with a true believer. Now I can just link to this instead of going off and chewing tree bark.

    I also watched, first, the other video in this series, A Digital Media Primer For Geeks. https://wiki.xiph.org/Videos/A_Digit...imer_For_Geeks Tough sledding for me, but good. On the "Talk" page (comments, click the "Discussion" tab at the top), again from the web page presentation, I found this nugget that explains once and for all why 44.1 was chosen. 48 would have been nice, but there would not have been any difference in the sound. Ditto for the true believers that claimed the problem with CDs was that the sampling frequency is too low; they thought 50kHz was the magic key. One more way to think they were smarter than Harry Nyquist...

    44100 Hz Trivia


    The reason CDs use a 44,100 Hz (actually 44,056 Hz in the United States) is because, before dedicated digital recorders became mainstream, the only way a recording engineer or producer could record digital audio was with a piece of gear called a "PCM processor" or a "PCM Adaptor" (like a Sony PCM-F1 of PCM-501). These would take an audio input and, after running through the A/D if necessary, it would modulate it onto a baseband monochrome NTSC or PAL video signal that could then be recorded onto a 3/4" U-Matic video tape. The processors would accept two inputs, at 16 bits, giving a total bit rate of 1411200 bps. This number has the serendipitous property of being evenly divisible by both 30 and 25, 47040 and 56448, and these numbers allow both NTSC and PAL to encode the same number of bits, 98, per scan line (with the NTSC 480 line raster and PAL 576 line raster). It was just convenient selection of integers. CDs would be recorded at 44.1k in Europe as they were mastered onto 25 fps tapes, while CDs in the US were recorded at a "nominal" 30fps were actually at 44.056, but the difference in tone is basically inaudible. Iluvcapra 18:44, 24 September 2010 (UTC)

    Note that the PCM audio signal, once modulated to NTSC or PAL, can be recorded on any video recorder, not just U-matic. The most common tape format for PCM audio was Sony Betamax. Sony sold Betamax decks bundled with external PCM A/D converter units for the pro audio market. The PCM-F1 was designed to be used with Betacam VCRs. -- Dryo

    I do think inches per second, not feet per second, was intended.
    Information is not Knowledge; Knowledge is not Wisdom
    Too many audiophiles listen with their eyes instead of their ears


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    Dang. Amateur speakerdave's Avatar
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    I knew it---SAUSAGE!
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    Senior Member edgewound's Avatar
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    Kinda, sorta....Pretty much...

    Quote Originally Posted by 1audiohack View Post
    I am away from a PC and hate writing via phone so please excuse the brevity.

    I spotted this link on ProSoundWeb. It reminded me of a conversation I had with Prof Doug Jones (currently working with Danley Sound Labs) a year or so ago about digital signals and processing.

    Take a look and give it a think. I would love to discuss it more, but from a key board!

    https://www.youtube.com/watch?v=cIQ9IXSUzuM

    All the best,
    Barry.
    ...lays to rest the idea that vinyl is superior to good ol' CDs.

    Great stuff, Barry. Thanks for sharing that!
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by edgewound View Post
    ...lays to rest the idea that vinyl is superior to good ol' CDs.
    Does it?

    A quiet record may only be the equivalent to 10-11 bits, but other than noise floor, I'm not convinced digital is superior.


    Widget

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    Quote Originally Posted by Mr. Widget View Post
    Does it?

    A quiet record may only be the equivalent to 10-11 bits, but other than noise floor, I'm not convinced digital is superior.


    Widget
    Which brings us back to something we barely discussed a few years ago - the engineering/mastering whatever on the CDs vs the albums. I'm not sure what the deal is, CDs are technically superior, but I tend to think what is put on the CD is (sometimes) inferior. If that makes any sense.

  10. #10
    Senior Member edgewound's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    Does it?

    A quiet record may only be the equivalent to 10-11 bits, but other than noise floor, I'm not convinced digital is superior.


    Widget
    Pretty much.


    From an absolute bandwidth and lack of noise standpoint, digital has much greater capabilities than analog...but the recording itself does matter. From the video that Barry posted, the looks of a sinewave between digital and analog are identical.

    This video is indicative of what most people prefer to listen to. That said, vinyl is a more romantic ritual...if you're into that.

    https://www.youtube.com/watch?v=HnxexlHRY2E
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  11. #11
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by edgewound View Post
    Pretty much.
    I'm pretty confident that a CD playing a 1KHz sine wave will look identical on a calibrated scope whether it is played on a $30 CD player or the high end player of your choice. I'm also confident that even a casual listener will hear differences between the two players when playing a well recorded CD of music played through a high quality system.

    Therefore digital audio accurately re-creating a sine wave tells us some information, but not the whole picture.


    Widget

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    Senior Señor boputnam's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    I'm pretty confident that a CD playing a 1KHz sine wave will look identical on a calibrated scope whether it is played on a $30 CD player or the high end player of your choice. I'm also confident that even a casual listener will hear differences between the two players when playing a well recorded CD of music played through a high quality system.

    Therefore digital audio accurately re-creating a sine wave tells us some information, but not the whole picture.


    Widget
    I've played with this more, of late, than for many years.

    I unearthed the turntable a while back and using a Radial J33 phono pre-amp (yes, I tried several - in my price range - and there are audible differences) I've been buying vinyl with CD combo packages the past year or so. I can compare audibly (A/B) the WAV files on the CD (thru Bryston BDA-1) with the same track off the turntable. To my hearing, there's no argument - the sonic quality of vinyl is not matched by CD. I suspect there is some characteristic(s) we are not measuring - perhaps not easily measured. That said, for convenience, the vinyl doesn't get sufficient listening time!

    Anyway, to argue the point is largely mooted by the convenience factor(s) alone. And, by the lack of WAF for larger-sized audio systems required for proper reproduction. So, I balance the want with the possible/needed. When it's my turn, it's vinyl - I happy to get up flip...
    bo

    "Indeed, not!!"

  13. #13
    Senior Member edgewound's Avatar
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    I'm honestly not trying to get into a pissing match over the merits of analog vs. digital, because they both have redeeming qualities in various sensory ways. A great recording is a great recording no matter the medium. Fact is, one of these mediums very handicapped by it's packaging.

    Here's an article that interviews some recording industry heavy-weights from both the art-making and scientific and production side of the topic.

    Hope you get a chance to read this. The two "Bobs", Bob Ludwig and Bob Clearmountain have pretty stellar credentials to have determining opinions on which is better technologically.

    http://www.laweekly.com/music/why-cd...-vinyl-5352162
    Edgewound...JBL Pro Authorized...since 1988
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  14. #14
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by edgewound View Post
    I'm honestly not trying to...
    And I want to put a full stop to the Analog vs. Digital debate on this thread. We have discussed it on others and will again, but this thread is about how digital audio works. I've moved several of these posts here.

    In my response to you I purposely left the analog comparison out of the conversation as I was only pointing out that the example shown in the video while compelling doesn't answer all of the questions.


    Widget

  15. #15
    Senior Member 1audiohack's Avatar
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    HI All!

    Thanks for the comments so far! Clark the 44100 trivia is just what I hoped this thread would bring. Widget, thank you for moving the D vs A debate elsewhere.

    I tend to work in the domains that I can cause effect, like DSP tuning and speaker building. I have not paid any real attention to how digital audio works because really, all I can do is choose to buy quality playback equipment and listen. Currently and for the last two decades my audio world has been all in the digital storage and playback domain.

    I have heard words like dithering and have until now had absolutely no idea what it meant, none, and I didn't care. The video taught me a ton.

    My experience with cheap verses quality playback devises mirrors Widgets. Here's a quote from Scott Helmke on the PSW conversation that may explains one possibility?

    "Years ago I had a Burr-Brown catalog with their 18-bit AD chips. The notes warned that you probably couldn't even get 16 bit resolution unless your analog circuitry was really carefully designed and laid out."

    And this from John Roberts:

    "I recall Burr-Brown being the big dog in DACs... Back in the day we would use a good reference DAC and then SAR (successive approximation register) to iteratively perform the A/D conversion. The layout and noise floor for this analog comparator comparing the reference DAC output to the analog input had to be less than 1 LSB or the conversion was unreliable.

    I recall way back last century when a junior engineer in the digital group at Peavey milked out one more bit from an early digital product's A/D conversion by cutting and rearranging some traces in the PCB. (His boss was not amused. )

    After Peavey I worked with one 16b codec that was extremely layout sensitive since there is both digital and analog circuitry inside the IC so integrity of different analog and digital grounds was important, just to realize the 16b performance. Most of the high bit codecs provide pro forma PCB layouts to follow."

    One more from John Ferreira:


    "This reminds me of very lengthy explanations and discussions on a audio forum 15 years ago or so, from a guy named Nika.

    Most people do not understand that one single bit can represent a full, complete wave form, and that used to cause the long arguments.

    The more bits, the further up from the noise floor, 6dB per bit. So, 16bit gives you 96dB of depth from the noise floor.

    Nika Aldrich ended up wrighting a book on this topic.

    EDIT: found it on Amazon:
    Digital Audio Explained: For The Audio Engineer Paperback – November 24, 2004
    by Nika Aldrich (Author)"


    A year or so in one of the conversations I had with D Jones, he told me something like: you just can't think of digital signal in an analog way. Once in the digital domain, it's all math, and it's the math that makes the most difference in how the D to A actually sounds.

    That might be absolutely true as long as the hardware mentioned above is correct. It is apparent that care, part quality and good engineering practice have an effect.

    In any event I am glad to have learned a bit more about digital and I'm looking forward to more.

    Thanks All!

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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