De-Emph

I tried playing a cd earlier, but the DAC seemed to have other ideas.

I've 4 leds on the left which indicate what freq it's at, then 2 on the left to indicate which input is on. And there's also one marked "DE-EMPH"

When I pressed play, the freq' leds were randomly flashing, and so was the DE-EMPH one

I had to turn the DVD off and than played the cd again. Worked fine then.

So, anyone know what DE-EMPH is? And why this happened?

 

I don't know what's causing your problems but I can explain what de-emph is

It's de-emphasis which is hardly ever used these days but in the early days of CD it was used rather like a sort of CD equivalent of the Dolby-B noise reduction you got on cassettes. Quite why anyone felt that CD needed noise reduction is beyond me

Basically, during the mastering of the CD the signal is compressed and then on playback, DACs that recognize the de-emphasis flag will de-compress the signal. btw, by compression here I'm not talking about MP3 style data compression but signal level compression to raise the average s/n ratio.

Michael.

 

There is a little-used option when recording CDs to use a couple of dBs of preemphasis (bit like the old phono days). On the rare occasion you played such a disc, coding in the data would tell the player the situation and it would obligingly remove the preamphasis and light the lampt to tell you (pointlessly) what was happening.

 

Thanks

I didn't think at the time, but the CD I was trying to play was a CDR.