Originally Posted by amirm
The data rate for "5.1" on toslink/coax is actually much less than stereo CD. The standard for compression in US for digital transmissions is Dolby Digital which is capped at 440 kbps (can go up to 640 kbps on Blu-ray). This compares to uncompressed CD at 1,400 kbit/sec or about three times higher! Yes, the sampling rate is usually 48 Khz for broadcast vs 44.1 for CD but lossy compression more than compensates for that.
The reason you may notice audio problems more with 5.1 is that compression occurs on a block of data at a time (called a frame). If you lose a few bits in that chunk, the decoder may throw out the entire frame. Further, the receiver may lose "synchronization" not knowing what is the start or the end of the frame. As a result of these factors, you hear a larger gap in audio when compressed 5.1 streams are transmitted and data loss occurs even though it is not taxing the link as much. In the case of playing uncompressed CD the lost data only impacts the specific audio samples and not the adjacent bits so the audible gap may be much smaller.
I was going to post the same thing. Amir has saved me a lot of typing.
In a nutshell, the link appears marginal, with just a few bits being dropped. With PCM, that means that individual samples are discarded, which are no larger than 23 microseconds and probably inaudible. With AC3 (and DTS), it prevents the entire block from being decoded, so you hear large drop-outs.
Although the problem is most likely the cable, it could also be the driver, receiver or dirt. If the cable was ever over-bent, that can permanently attenuate the light passing through it.Edited by MarkHotchkiss - 11/20/12 at 11:59am