In Reply to: RE: USB cable errors - NOT posted by AbeCollins on August 26, 2014 at 12:02:18:
"How would hard data errors and the lack of retries manifest themselves audibly in the audio playback chain?"There are two possibilities:
1. process the erroneous data. What you get is what you hear.
2. ignore the erroneous data and attempt to guess what it was. What you hear depends on the algorithm.In the case of SPDIF there is no further error detection, so it's case 1. You will hear clicks, amplitude depending on which bits in the PCM word get corrupted.
In the case of CDA (Red Book coding) there is a strategy to correct errors and to guess at single sample uncorrectable errors by interpolation, otherwise to mute. Most single errors are successfully interpolated without clicks. There are test tools that CD mastering engineers run to evaluate the quality of the raw bits on a disk to see what margins for error correction remain.
With USB audio, the DAC would implements some kind of strategy. I suspect this includes discarding any packets that have CRC errors. Here error detection is done on a packet basis which contains roughly 1 millisecond of audio. One can simply duplicate the missing sample or one can drop it and slip the tempo one millisecond, etc... If this doesn't happen too often it won't be noticeable on most music to untrained listeners. (The details will depend on the particular USB protocol the DAC uses, which may be proprietary.) The aural effects are likely to be similar to buffer underruns due to computer system overload. One strong reason for discarding packets that fail the CRC concerns the USB frame format. Bit stuffing is used to delimit the data packets, which means that a single bit in error can turn into a different number of bits in the output, resulting in loss of PCM word framing. If PCM framing is lost the results can be a horrible (if not dangerous) burst of noise.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- RE: USB cable errors - NOT - Tony Lauck 08/26/1413:36:35 08/26/14 (35)
- RE: USB cable errors - NOT - AbeCollins 16:16:23 08/26/14 (34)
- RE: USB cable errors - NOT - Ugly 06:27:34 08/27/14 (33)
- RE: USB cable errors - NOT - AbeCollins 07:54:51 08/27/14 (32)
- RE: USB cable errors - NOT - audioengr 10:32:51 08/27/14 (1)
- RE: USB cable errors - NOT - AbeCollins 12:03:35 08/27/14 (0)
- RE: USB cable errors - NOT - Ugly 09:30:16 08/27/14 (29)
- this is a protracted discussion of no substance. - fmak 01:13:36 08/29/14 (1)
- It is clearly the hand of God typing at your keyboard and no mere mortal. - Ugly 06:42:11 08/29/14 (0)
- Understand. - AbeCollins 12:06:40 08/27/14 (26)
- RE: Understand. - rick_m 08:37:54 08/29/14 (25)
- RE: Understand. - Ryelands 09:24:42 08/29/14 (24)
- RE: Understand. - AbeCollins 22:41:12 08/29/14 (22)
- RE: Understand. - Tony Lauck 12:10:37 08/30/14 (6)
- Here you go...... - AbeCollins 13:10:42 08/30/14 (4)
- RE: Here you go...... - Tony Lauck 13:34:00 08/30/14 (3)
- RE: Here you go...... - Ryelands 13:59:52 08/30/14 (2)
- RE: Here you go...... - AbeCollins 18:33:59 08/30/14 (1)
- RE: Here you go...... - Tony Lauck 18:58:14 08/30/14 (0)
- So, in other words, without trying to be needlessly polite, it - ... - carcass93 12:28:15 08/30/14 (0)
- RE: Understand. - Ryelands 01:43:13 08/30/14 (14)
- RE: Understand. - AbeCollins 07:15:00 08/30/14 (13)
- RE: Understand. - Ryelands 07:47:59 08/30/14 (12)
- RE: Understand. - AbeCollins 08:26:29 08/30/14 (11)
- RE: Understand. - Bob_C 18:58:49 08/30/14 (10)
- RE: Understand. - Tony Lauck 19:29:25 08/30/14 (5)
- RE: Understand. - AbeCollins 21:51:37 08/30/14 (1)
- RE: Understand. - Tony Lauck 09:05:59 08/31/14 (0)
- RE: Understand. - Bob_C 19:40:41 08/30/14 (2)
- Hey, that's not fair - how come I don't get called Saint something? - carcass93 08:54:33 08/31/14 (1)
- RE: LMAO!!! nt - Bob_C 09:39:08 08/31/14 (0)
- Huh? - AbeCollins 19:26:25 08/30/14 (3)
- Guilty I am! - rick_m 11:05:32 08/29/14 (0)