CD Pre-emphasis
03-30-2014, 07:38 AM,
Post: #1
CD Pre-emphasis
http://wiki.hydrogenaudio.org/index.php?...e-emphasis

When ripping a CD, it apparently is important to know if pre-emphasis was applied to the PCM data or not. This was a noise reduction technique used in the early days of CD mastering when many ADCs only were 14-bit capable and did not over-sample.

It still is apparently used by some indie labels.

I'll have to figure out how to detect it in my ripping process, recent versions of iTunes automatically detect it and apply a de-emphasis filter if needed. Older versions of iTunes did not. But with command line rippers, it needs to be passed through something like six with the deemph filter to get the proper sound.

I suspect I do not have very many CDs that used this, hopefully the information would be stored in the TOC and other non-audio info I save when I rip.
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03-30-2014, 07:43 AM,
Post: #2
RE: CD Pre-emphasis
Really? Fascinating.
03-30-2014, 07:50 AM,
Post: #3
RE: CD Pre-emphasis
(03-30-2014, 07:43 AM)more or less Wrote: Really? Fascinating.

Well not fascinating as much as some CD rips may not be result in audio data that results in the intended playback.
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03-30-2014, 09:21 AM,
Post: #4
RE: CD Pre-emphasis
database++
03-30-2014, 03:02 PM,
Post: #5
RE: CD Pre-emphasis
okay iTunes does not always get it right.

Most CDs that have it indicate it both in the bistream and in the TOC.

Some only do one or the other.

If the CD indicates pre-emph in the TOC, iTunes will get it right.

However if the CD only indicates it in the bitstream, iTunes will not detect it and rip it wrong, it will sound "brighter" than intended.
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03-30-2014, 05:25 PM,
Post: #6
RE: CD Pre-emphasis
Tom Petty & Heartbreakers - Southern Accents - it is a CD that has pre-emph (at least mine does, only one I've found so far that does)
Here's visual difference -

[Image: deemph_zpsab8464a6.png]

It's subtle, bottom is what it is suppose to be.

On my PC with cheap speakers I can't hear. On stereo I can, and corrected is better.
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03-30-2014, 06:44 PM,
Post: #7
RE: CD Pre-emphasis
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03-30-2014, 09:56 PM, (This post was last modified: 03-30-2014, 09:57 PM by FunkyRes.)
Post: #8
RE: CD Pre-emphasis
Another old mastering trick I wasn't aware of - not used very often, but used nonetheless.

With integer PCM digital audio, the smallest positive number is 10000000 00000000
The smallest negative number is 01111111 11111111

With early DACs, some of them were very poor at switching between the two resulting in a click.

This transition from positive to negative would happen at the median baseline, the 0.0 in the image above, and was very audible during quiet parts of the audio.

So some mastering studios would intentionally add a DC offset so that the median baseline was no longer at 0 volts. The result is the clicks from sub-par ADCs were more likely to occur during high amplitude loud parts of the audio that would mask them. Low amplitude quiet parts were above 0 volts.

One downside is that manually changing tracks would often result in a loud pop, and another downside is you had less headroom, your peak volume could not be as loud without clipping, but they usually recorded with quite a bit of headroom in 16-bit domain because back then, they couldn't record at higher bit depths, normalize, and then re-sample for the CD. The techniques did not exist. In fact often they recorded at 14-bit.

It was a really ingenious technique that allowed the audio to still sound decent with sub-par DACs.

Nowadays it isn't needed anymore, even the cheapest DACs don't have the click problem, and when ripping a CD that was mastered this way, it is a good idea to remove the DC offset before encoding in whatever coded you want - if you peak normalize before encoding, that usually automatically fixes the offset, but it depends upon the software you use.

I believe sox with the --norm option does but I haven't tested it, I will probably have to create a wav file with DC offset to test as I don't believe I have any CDs that used this technique.

It was a brilliant idea for its time though (early 80s)
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03-30-2014, 10:13 PM, (This post was last modified: 03-30-2014, 10:14 PM by FunkyRes.)
Post: #9
RE: CD Pre-emphasis
And back to pre-emph - at least historically the de-emph was applied analog after the DAC and that is why a CD would often sound different in different players. CDs that did not use pre-emph generally sounded the same, but the de-emph used varied from player to player as it was analog.

I'm not sure what modern CD players do (they still have to apply de-emph if the track has pre-emph, it's redbook), now they may do it digitally in the DSP before the conversion to analog, but it was analog in the 80s.
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03-31-2014, 02:32 AM,
Post: #10
RE: CD Pre-emphasis
lol


Attached Files Thumbnail(s)
   
03-31-2014, 03:03 AM,
Post: #11
RE: CD Pre-emphasis
OMG DID U KNOW NOT ALL CD ROMS AND RIPPING SOFTWARE COMBINATIONS SUPPORT DAE!

DO U KNOW IF UR RIPS WERE DAE OR ANALOG CONVERSIONS!??

OMG OMG OMG
03-31-2014, 04:06 AM, (This post was last modified: 03-31-2014, 04:08 AM by more or less.)
Post: #12
RE: CD Pre-emphasis
WHAT IF YOU RESAMPLED!?

OMG AT WHAT POINT IN THE AUDIO SIGNAL PATH DID YOU RESAMPLE TO 48K!!??

DID IT TAKE RAW LPCM DIRECTLY FROM THE CDDA FORMAT AND HAND THE PCM DATA DIRECTLY TO THE ENCODER, OR DID IT CONVERT TO PCM TO PWM AND BACK AT FORTH FROM THE DAC TO THE ADC AT SOME POINT. DID THE DSP AFFECT THIS PROCESS!?

OMG OMG OMG
03-31-2014, 04:06 AM,
Post: #13
RE: CD Pre-emphasis
um what?
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03-31-2014, 04:11 AM,
Post: #14
RE: CD Pre-emphasis
OMG I BET YOU DIDN'T COMFIRM IF YOU DIRECTLY ENCODING THE RAW LPCM DATA OR TRANSCODING FROM PWM!!!
03-31-2014, 04:25 AM,
Post: #15
RE: CD Pre-emphasis
um what?
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03-31-2014, 04:33 AM,
Post: #16
RE: CD Pre-emphasis
OMG WHAT CLASS OF AMPLIFIER ARE YOU USING?

WHAT QUALITY CABLES ARE USING TO TRANSMIT THE AUDIO?

HAVE YOU WHITE NOISE AND PINK NOISE FREQUENCY TESTED THE AUDIO ENVIRONMENT TO ADJUST FOR ANY INHERENT FREQUENCY OR NOISE BIASES YOU MAY BE INTRODUCING?

OMG OMG OMG
03-31-2014, 04:38 AM,
Post: #17
RE: CD Pre-emphasis
(03-31-2014, 04:25 AM)FunkyRes Wrote: um what?
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03-31-2014, 04:42 AM, (This post was last modified: 03-31-2014, 04:42 AM by more or less.)
Post: #18
RE: CD Pre-emphasis
OMG WHAT IF YOU PLAY AN UPSAMPLED 24bit 48.1K FILE ON AUDIO ON A DEVICE THAT ONLY SUPPORTS NATIVE 16bit 44.1 AND HAS TO TRANSCODE THE PADDED AUDIO FILE BACK TO ITS ORIGINAL BIT DEPTH!?

OMG OMG OMG
03-31-2014, 04:44 AM, (This post was last modified: 03-31-2014, 04:44 AM by FunkyRes.)
Post: #19
RE: CD Pre-emphasis
(03-31-2014, 02:32 AM)more or less Wrote: [Image: attachment.php?thumbnail=105]

Clearly there are none so blind as those that will not see.
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03-31-2014, 04:49 AM, (This post was last modified: 03-31-2014, 04:50 AM by more or less.)
Post: #20
RE: CD Pre-emphasis
OMG ARE USING CLASS A, CLASS B, CLASS A/B, CLASS D OR CLASS T TYPE AMPLIFIERS!?

ARE USING TOSLINK OR COAX?

ARE YOUR SPEAKER CABLES THE PROPER GAUGE?

WHAT OHMS?

WHAT WATTAGE?

WHAT SPEAKER CONE DESIGN AND MATERIALS ARE YOU USING?
03-31-2014, 05:06 AM,
Post: #21
RE: CD Pre-emphasis
Your lips are moving. That's a problem.
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03-31-2014, 05:24 AM,
Post: #22
RE: WebVTT
ARE YOU USING IRON-FERRITE OR NEODYNIUM MAGNETS?

HOW ARE YOU SPEAKER CABLES CONNECTED TO YOUR AMP? ARE YOU USING CUSTOM CABLES OR PREWIRED RCA TYPE CONNECTORS? DID YOU SOLDER THE ENDS?

WHAT DISTANCE ARE YOU FROM YOUR SPEAKERS AND WHAT IS THE SHAPE OF YOUR LISTENING ROOM?

HOW MANY SPEAKERS ARE YOU USING?

WHAT TYPE OF SPEAKERS AND SPEAKER CABINETS ARE YOU USING?
04-01-2014, 12:18 AM,
Post: #23
RE: CD Pre-emphasis
I like to listen to music.
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04-01-2014, 02:53 AM,
Post: #24
RE: CD Pre-emphasis
WHAT'S A CD?
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04-01-2014, 05:06 AM,
Post: #25
RE: CD Pre-emphasis
(04-01-2014, 02:53 AM)roo Wrote: WHAT'S A CD?

A CD is a time deposit with a bank. They bear a specific maturity date (from three months to five years), a specified interest rate, and can be issued in any denomination, much like bonds.


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