A lot of users complain that when used as USB DAC, N5ii exhibits delays and/or cannot synchronize with the video signal on the computer. This will affect the user experience when lip-syn (movie, MTV) or special sound effect (computer game) is an important feature. Unfortunately this problem cannot and will not be modified through firmware upgrade.
N5ii is a digital audio player and we put audio performance as our primarily objective. To ensure we have best possible USB Audio performance, N5ii operats in Asynchronized USB transmission, I shall quote the following explanation on
asynchronous USB for discussion purpose:
"Asynchronous USB (not to be confused with asynchronous samplerate conversion) uses a clock housed near the dac (usually in the external dac’s casing) and allows it to drive the converter directly, thereby not relying on the instable computer’s clock. It is called asynchronous because the DAC’s master clock isn’t synchronized directly to any clocks within the computer. Instead, the DAC is controlled by a (potentially high-precision) fixed-frequency clock. This clock controls the datastream from the computer to a buffer near the DA converter."
I would like to draw your attention to two issues in this explanation:
- the DAC’s master clock isn’t synchronized directly to the clock of the digital source (a computer in most of the cases)
- This controls the datastream from the computer to a buffer near the DA converter
In other word, the audio signal processing is deliberately "disconnected" from the computer clock but the video display remain connected to the computer clock, so the video and audio are not synchronized by nature. In addition, we need to create a data buffer in the audio circuit in order to hold the audio datastream from the computer, and the buffer will inevitably caused delays in the audio signal with reference to the non-buffered video signal. For the record, IEE1394 Firewire was considered the only acceptable option to connect a computer device to an high end audio back in the 90s, USB was not consider acceptable as those were the time when USB connection was operated in synchronized mode and the extremely high jitter and occasional drop out is consider unacceptable by audiophile. The Asynchronized USB transmission has solved these inherited problem and gradually replaced the IEEE1394 Firewire connection in high-end audio, it become the necessary (but not sufficient) criteria to use USB for high quality audio application.
If you must achieve audio and video synchronization, you can do that by adding a delay in the video reproduction. Most Home Theater system will have to handle similar issues and they call it lip-sync, this can be a DSP feature in the Audio-Visual Control Center (Receiver) or a video delay adjustment in the LCD TV or projector, so please check your computer monitor to see if similar feature is in place.
Click to expand...
