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Old 22nd January 2013, 06:20 PM   #21
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Digital has come a long way. My first experience was in early 1980s working on even-then antique (1950s?) teletype tecnology. I learned about mark/space, polar, neutral and also not to touch the DC voltages. Technically no error correction but when the circuit dropped the printer "ran open" (ker-chunk but printeth naught). Also was fun to **** off the next station by holding down "bell" and "repeat" DINGETY DINGETY DINGETY DINGETY ETC. In some ways the old tech was better. Ah, for the smell of machine oil and cheap rolls of paper. 5-level BAUDOT anyone?

More apropos to this discussion, in tech school we learned about many possibile types of distortion to the digital signal. In practice, we very rarely encountered these. For the rational, there are ones and zeros. For the audio-fool, there are $200 special cables to make the ones "oner" and the zeroes "zeroer."
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Old 22nd January 2013, 06:49 PM   #22
GoatGuy is offline GoatGuy  United States
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Default Isochronous USB ... myths, realities...

Quote:
Originally Posted by counter culture View Post
Most USB audio devices of generations ... use isochronous transfer, where there is no provision for retransmission in the case of errors. Isochronous clocking depends on the host's clock, the data is transmitted willy-nilly, and the DAC must adapt its clock to accommodate the transmitted data rate, usually using a PLL. ...
Umm... not quite.

The isochronous data transmission mode remains a packetized data transfer mode, where whatever native audio digital information rate is buffered, then squirted out at USB2 bitrates, but in an isochronous transmission window whose opening is guaranteed within a microsecond or so.

Further, digging a bit, I find that for audio it remains an uncorrected/unprotected data stream, implementing a derivative of the AES/ADAT bit-coding scheme for data transmission. Therefore, what I said regarding data-drops, loud squarkings and so on, remains true. If you're hearing seemingly un-grossly tarnished audio at all, then you're hearing error-free audio. Since the PCM/digitization technology is completely encapsulated by the much faster bit-packet-stream, by definition, ALL playback devices must employ buffering and down-rate conversion.

But thanks... I get what you're talking about.

GoatGuy
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Old 22nd January 2013, 06:55 PM   #23
marce is offline marce  United Kingdom
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Goatguy, by the way is your monika a grown up Goatboy (RE: Bill Hicks, c1993)
Were not all as dumb as you may think, even those of us who believe (know) that digital is 0s and 1s, and here I consider myself a life member of that camp...why because I spend all day making sure digital signals get from a to b, including signal integrity simulation.
The digital waveform may (will) get distorted to some extent (look at DDR memory waveforms), but the end result is a signal that will be interpited as either a 1 or a 0.
For the uninitiated I suggest getting "Signal Integrity simplified" Eric Bogatin or Howard Johnsons book, some good reading.
The misunderstanding of digital signal transmission in some circles (Audio) is quite amazing, a recent thread comes to mind, when someone pointed out that moving files around your system can add low level distortion to the digital data, the poster stated it as a fact and refused to discuss the matter further (but did quote a couple of audiofile gurus, who had also noticed this... (CRC gives the same results, you can only hear this low level distortion).
Of course if the cable is naff, you will get lots of naff packets and data will have to be re-transmitted.
Digital signals are pretty immune to the distortions that they suffer, the worse one is non-monotonicity on the rising or falling edges.
Have fun all
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Old 22nd January 2013, 07:00 PM   #24
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I will believe in superiority of some data cables when it will be proven in the computer world. Otherwise I believe in the crappiness of some USB audio interfaces where listener can hear the difference between the cables. The cable is the last problem in such cases
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Old 22nd January 2013, 07:08 PM   #25
GoatGuy is offline GoatGuy  United States
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Quote:
Originally Posted by marce View Post
Goatguy, by the way is your monika a grown up Goatboy (RE: Bill Hicks, c1993)
Were not all as dumb as you may think, even those of us who believe (know) that digital is 0s and 1s, and here I consider myself a life member of that camp...why because I spend all day making sure digital signals get from a to b, including signal integrity simulation.
The digital waveform may (will) get distorted to some extent (look at DDR memory waveforms), but the end result is a signal that will be interpited as either a 1 or a 0.
For the uninitiated I suggest getting "Signal Integrity simplified" Eric Bogatin or Howard Johnsons book, some good reading.
The misunderstanding of digital signal transmission in some circles (Audio) is quite amazing, a recent thread comes to mind, when someone pointed out that moving files around your system can add low level distortion to the digital data, the poster stated it as a fact and refused to discuss the matter further (but did quote a couple of audiofile gurus, who had also noticed this... (CRC gives the same results, you can only hear this low level distortion).
Of course if the cable is naff, you will get lots of naff packets and data will have to be re-transmitted.
Digital signals are pretty immune to the distortions that they suffer, the worse one is non-monotonicity on the rising or falling edges.
Have fun all
We seem to agree. "GoatGuy" is from generally being a technical billy-goat - in that I like to take the opposite side of most arguments (unless it is clearly just wrong). Yes, I remember Goatboy.

Non-monotonicity in rising/falling edges in the digital stream is one of the most significant factors that introduces phantom bits into a NRZI encoded bitstream. "wise" decoder (demux) devices though don't trigger on the edge, but capture the prevailing J/K bit state of the PREVIOUS transition at the edge. This is far less susceptible (at least 2 and some say up to 4 orders of magnitude) to nonmonotonicity than rising edge issues.

GoatGuy
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Old 22nd January 2013, 07:39 PM   #26
Makk is offline Makk  Finland
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How about this kind of USB signal transfering?
Air DAC
What do you think? Is it as good as cable or even better?
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Old 22nd January 2013, 07:43 PM   #27
GoatGuy is offline GoatGuy  United States
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If the bitstream gets there unmangled by transmission over the radio wave bands, then I can see little wrong with using the device.

GoatGuy
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Old 22nd January 2013, 07:58 PM   #28
Makk is offline Makk  Finland
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Yep, but for some reason I believe more in cables.
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Old 22nd January 2013, 08:06 PM   #29
GoatGuy is offline GoatGuy  United States
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Quote:
Originally Posted by Makk View Post
Yep, but for some reason I believe more in cables.
And I too... nominally.

There is something particularly sexy though about having a wireless fabric over which to move the digital sound data.

One can move their "iDevice" about, keep it in pocket, not needing to even connect it when coming back from a long day trip. Sure a cable works. But if the wireless approach actually WORKS (i.e. through encoding and other means, achieves a near-zero bit-error-rate), and if one is committed to spend "in the hundreds" for a fine (or I say, too fine) cable... then why not?

GoatGuy
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Old 22nd January 2013, 08:09 PM   #30
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Looks like this is the thread for USB audio virgins

Come on guys, do just a bit of research on async transfers as pioneered by Gordon Rankin and pretty much the standard today and the amazing thread about Ian's FIFO.
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