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Topic: Applying pre-emphasis (Read 1317 times) previous topic - next topic
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Applying pre-emphasis

I thought this could be something worth trying for converting audio to burn onto a CD, but it's more complicated than I thought.
The one thing that I have tried but didn't work is using SoX with the following sequence of commands, but it didn't give me an output anywhere close to the original:
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sox.exe .\Original.wav De-emphasis.wav deemph vol -1
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sox.exe -m .\Original.wav .\De-emphasis.wav Emphasis.wav
Code: [Select]
sox.exe -m .\Original.wav .\Emphasis.wav Pre-emphasis.wav
and then to test if it's close to the original:
Code: [Select]
sox.exe .\Pre-emphasis.wav De-emphasized.wav deemph
which, as I already mentioned, wasn't.
So is there actually a way to do this without doing it backwards (and failing it like that)? Everything else that I found was for applying de-emphasis.

Re: Applying pre-emphasis

Reply #1
ffmpeg have filter for both directions called aemphasis.
Please remove my account from this forum.

Re: Applying pre-emphasis

Reply #2
Pre-emphasis and de-emphasis on CDs is optional and VERY RARE.    As far as I know, I don't have any CDs with pre-emphasis.

I've NEVER heard of ANYBODY burning a CD with it and your burning software would have to know how to set the flag to trigger de-emphasis when it's played.    

If you have a good WAV file at 16-bits, 44.kHz, stereo, and you burn an Audio CD you can play it (or rip it) bit perfectly without emphasis.   

Pre & de-emphasis is never bit-perfect end-to-end, but it should sound perfect if done correctly.


...Usually, when you rip a CD that has emphasis, it's not de-emphasized automatically and you have to do that as a separate step after ripping.     

Re: Applying pre-emphasis

Reply #3
Sure, applying pre-emphasis to your own burned CDs doesn't serve much purpose apart from testing.
I keep my pre-emphasis CD rips as they are, applying the de-emph curve on-the-fly with a component: https://hydrogenaud.io/index.php/topic,99394.0.html , give the files a tag <PRE_EMPHASIS> with value 1.

There are a few in my collection, actually. As far as I can see, the most recent recording was 2007. (But I haven't bought that many physical CDs with newer recordings.)

You are more likely to get pre-emphasis CDs if you pick up old pressings 2nd hand (why? Because those pre-loudnesswar masterings are unavailable elsewhere!) A couple of lists, including artists like Miles Davis, Pink Floyd, Bruce Springsteen, Black Sabbath and Genesis: https://www.studio-nibble.com/cd/index.php?title=Pre-emphasis_(release_list)  and https://www.discogs.com/lists/Pre-Emphasis-CDs/581360?page=1&limit=250
Also, for classical music, some labels buy old masters, warts and all, no questions asked. Sometimes you get well-reputed recordings that way, like that is how I got Hans Fagius' recordings of Bach's organ works, originally recorded for the BIS label; and with pre-emphasis.
Also certain labels like Cold Meat Industry seemed to enjoy the pre-emphasis disease.

Re: Applying pre-emphasis

Reply #4
Theoretically it's possible to levarage more dynamic range using this, especially combining it with shaped dither, with the obvious downside that there's a possibility that different players will have noticeably different sounding filters, or may be lacking them entirely. So yeah, moreso just a bit of "fun" on my end.
Just to clarify, I'm obviously not going to use this for burning audio that's already CD quality (unless I'm doing some form of processing to it which would increase its bit depth, I suppose, which is most processing), just for converting hi-res audio down.
So thanks to mycroft for telling me about ffmpeg's filters, albeit it wouldn't've been a problem had I not forgotten about them.
Edit: Oh, and as for CD burners having the capability to burn with pre-emphasis flags, it should probably be implemented as a standard feature, since otherwise how would you burn tracks from CDs which had pre-emphasis (without converting them obviously)?