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Learned something new today and it isn't good.

I have been in this crazy hobby for over five decades and thought I knew most of the basic information regarding audio quality.

That was before this morning.

Today I learned about the practise of applying "pre-emphasis" to CDs that was around during the late '70's and early '80's. Apparently this practise was developed as a way of reducing the signal to noise in digital audio. The problem is this was a two-part process and required the CD player to have a "de-emphasis" capability to allow the disk to play properly. Without the application of de-emphasis, cd's would sound "bright".

My question would be, "Does everyone else know about this?"

If you do, "How do you deal with it?"

I still listen to CDs and this is not something I need in my life.

128x128tony1954

Showing 2 responses by thespeakerdude

thespeakerdude
483 posts
 

Please don't ask me to explain this in any more detail as I will already be pushing the limits of my knowledge. Use Google if you want to learn more.

Nyquist rate DACs have a zero-hold structure. They are not flat to 20KHz and roll off towards 20KHz. A zero-hold means it holds the same value between sample updates. I understand ADCs don't normally have this issue because they take a snapshot in time. To compensate for this roll-off, the CD could have pre-emphasis to compensate and get a flat response. The roll off is not very big. When up sampling DACs became standard, this was not needed as the roll-off at 20KHz was very small.

The redbook CD standard has a flag on the CD that says pre-emphasis was applied. The CD player should read this and tell the player what it needs to do if anything.

thespeakerdude
483 posts
 

This has nothing to do with noise or noise reduction. Why does that keep getting repeated??

It was a necessary step to deal with the natural operation of early DACs.

One of my colleagues sent this. It is not light reading but the concept seems easy to understand.

https://www.analog.com/en/technical-articles/equalizing-techniques-flatten-dac-frequency-response.html

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