analog_sa said:
Refreshing is the word. Where else would you find so many opinions based on zero first hand experience with actual USB dacs and cables.
But so much common sense
Bits are bits! If i don't know what's jitter, no way you can hear it.
Look in the datasheet for a TI PCM2707 or any other USB DAC/receiver, and you will see a FIFO buffer and a self generated clock. As long as there is data in the buffer, the USB data speed or variations thereof (jitter) relates in no way to DAC output jitter.
analog_sa said:
IP was not design for high end audio either, yet it can be used for that to great effect.
There are 2 issues here for USB:
1) USB audio does not retransmit corrupted frames, so data can be lost.
- This is also a problem with SPDIF, but on a grander scale since a corrupted USB packet is a much larger data loss than bit errors on SPDIF. A better solution would be retransmission of corrupted frames, as is the case with USB bulk transfers. It would not be as convenient to implement (no existing ASIC+standard drivers), but you also get much higher data rate possibilities in the bargain.
- USB audio is not a great spec. USB can still make a perfectly good audio transport, though.
2) USB audio implementations often have poor clocking.
- Assuming there is no packet corruption on the link, reclocking at the USB DAC should make USB-induced jitter irrelevant. If this is not the case, I'd love to hear why not as, if it doesn't help here, it shouldn't help anywhere else.
I haven't seen anyone argue that there can't be cable-induced jitter for USB audio, that seems plain enough. The USB jitter specs are rather wide, as well. What I have seen is a group of folks, including me, saying that properly implemented USB DACs will be effectively immune to cable jitter. The alternative would seem to be that, regardless of how it is implemented, USB DAC quality is dictated by the quality of the cable.
planet10 said:
What in the specifications do you believe means FireWire produces a better result than USB 2.0? It might be easier, there might even be existing silicon to help you along, but I'm not seeing the better quality part.
edit - I should be more clear to avoid the armies of pedants: I know FireWire to transport media, I just don't think it matters once you have so much more bandwidth than is required to transport the media in question. Putting 24/192 audio across a 480Mbps or 400Mbps stream just isn't much of a challenge.
I'm glad to see that the "cable can make no difference" believe has changed to the "usb dac is not good enough" believe.
Perhaps the latter is true but keep in mind that the poor guys with their cables can only use equipment that is commercially available, so if cable make a difference in that case, then it work. If they are willing to pay that much for it, it's their money.
Interesting to note the same pattern every time I see a cable debate, ironically the non believers have never tried it themselves but they seem to know everything about the subject.
André
Perhaps the latter is true but keep in mind that the poor guys with their cables can only use equipment that is commercially available, so if cable make a difference in that case, then it work. If they are willing to pay that much for it, it's their money.
Interesting to note the same pattern every time I see a cable debate, ironically the non believers have never tried it themselves but they seem to know everything about the subject.
André
b-square said:
Sorry for being a bit slow, but feeding which part with a quality clock? A 2707? The 12MHz clock?
From what i understand this clock is mostly responsible for the USB framing, rather than the recovered clock. Incidentally i have tried a better quality clock there and it did bring some minor improvements.
Andre Visser said:
You have misunderstood, it seems. The arguments I, and others, have made is not that the cables don't matter. On the contrary, I agree they can make a difference. If cables do make a difference in this application, then there is a problem in the DAC. I also believe the same thing about SPDIF interfaces. Cables can make a big difference if the transmit or receive implementation is poor. In good implementations, the cable makes little difference.
If people prefer to spend the money on cables instead of properly implemented components, that is absolutely their business. Interesting that those same folks seem to be awfully sensitive about questions people raise about their decisions, though. I wonder why that is.
Achieving High-End computer-based playback is basically no different from CD-based High-End playback.
This is required:
1) Bit perfect playback (computer hardware / OS / drivers / applications).
2) Lowest possible jitter that does NOT correlate with interface jitter, measured directly at the DAC chip timing input (same solutions as with CD-based systems apply).
3) Full galvanic insulation between both computer and DAC (TOSLINK / optically-insulated USB / SPDIF coax, using pulse transformers with very low coupling capacitance, or a high-speed opto-coupler).
IF digital interface cables DO make a difference in sound quality, the problem is either a poorly designed DAC (sensitive to interface jitter), or an unwanted galvanic connection between both computer and DAC digital interface receiver (noise / interference / ground loops).
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.