Digital de-emphasis

[eisenach]

Maybe some of you technical people can explain this to me !

I've just moved my Tag Mclaren DAC20 from the second system to the main, where it mainly looks after the satellite box and the mini-disc player. When getting its signal from the satellite box, the de-emphasis led is coming on, whereas it never did in the other system.

The satellite boxes are different makes, but the signal coming off the satellite (Antlantic Bird 3) is the same. Can anyone explain what's going on ?

[AlexM]

Digital de-emphasis is almost never found on CDs - it was included in the red book CD standard to allow 14 bit digital recordings to be encoded with reduced quantisation noise. Maybe your satellite receiver audio bit stream was originally encoded from a lower bit depth (such as NICAM), and the pre-emphasis was applied to reduce noise. Is the LED lit all of the time, or just for certain programmes?.

Nothing to get too concerned about in any case IMHO...

Regards,
Alex

[eisenach]

Just curious as why one box should cause the de-emphasis light on the dac to come on and the other not when they're both dealing with the same original signal.

[AlexM]

Ah, sorry. I misunderstood your post. The answer is probably simply that either one receiver is ignoring the de-emphasis flag in the stream and bleaching it internally before sending it to the digital output, or more likely that it is applying de-emphasis during decoding whereas the other receiver is passing it through to the digital output without processing. It shouldn't affect the sound greatly whether the receiver processes the de-emphasis or whether your TAG does it.

Hope this helps.

Alex