Music, Digital Compression and Compact Discs
therockman
Posts: 349
Digital maximization and digital compression are two forms of interrelated digital distortion that is applied intentionally to the music stored on compact discs. The technical ability to "crank up the volume" (digital maximazation) and to level out the dynamics (digital compression) results in a louder disc that plays loud all the way through, without the dynamic range normally associated with the natural reproduction of music. It is easy to understand the technical aspects of these two intentionally applied distortions if one knows a little bit about digital mastering for the compact disc.
__First of all, all music begins life as an analog signal. When music is converted into a digital stream of information ready to be transferred to compact disc, the music has to undergo a A/D (analog to digital) conversion. This A/D conversion requires that the original analog signal that represents music undergo a process called "sampling" and "quantization". Sampling and quantization are the cornerstones of digital audio and are actually distinctly different but interrelated processes which work to covert music from an analog signal into a series of numbers.
The analog signal that represents music exists as a voltage that varies over time. The faster the signal varies over time, the higher the audio signal's frequency, (this is represented as "time information"). The greater the amplitude of the signal, the louder the signal is. Sampling and quantization is the process of producing a series of binary numbers, called "words," that represent the analog waveform. An A/D converter encodes the signal's time information by sampling the analog audio signal at discreet time intervals and assigning a numerical value to this information. The amplitude information is encoded by generating a number that represents the analog waveform's amplitude.
The combination of this "time information" and the amplitude information is stored as a binary word in the digital realm. Thus, when the binary words are converted back into voltages, the analog audio waveform is roughly reproduced.
Quantization is the most important factor of the A/D conversion process that allows an engineer to digitally maximize and compress the audio signal. It has to be remembered that quantization is simply the generation of a binary number that represents an analog waveform's amplitude. In other words, the binary number that is generated through the process of quantization is a digital representation of the audio signal's analog voltage when the sample is taken. It is easy for an engineer to increase the binary number that represents voltage, thus increasing the amplitude of the audio signal. This process is called "digital maximazation." The process of adding a like amount of digital amplitude information to the entire digital sample (a song for instance) is called "digital compression." By subjecting a digital sample of recorded music to the interrelated process of digital maximazation and digital compression, an engineer ends up with a louder piece of recoded music that plays loud all the way through. This final product is now suitable for radio playback because the artist will now have the loudest song on the radio.
The only problem with the final product is that now the music doesn't have a natural waveform. A sine wave should roll naturally, with nice round tops and bottoms. Through the process of digital maximazation and digital compression, the engineer creates a waveform that is clipped at the peaks (top and bottom) and our ears perceive this clipping as distortion. This is the reason that most "older people" find new music irritating and they get tired listening to new music real quickly. It is not necessarily the music itself that is irritating them, it is the way it is reproduced.
So there you go. This is the story of digital maximazation and digital compression. Even though an audiophile has invested a great amount of time and money into their system, a new CD will still sound terrible simply because of the distorted waveforms that we are reproducing through our systems.
__First of all, all music begins life as an analog signal. When music is converted into a digital stream of information ready to be transferred to compact disc, the music has to undergo a A/D (analog to digital) conversion. This A/D conversion requires that the original analog signal that represents music undergo a process called "sampling" and "quantization". Sampling and quantization are the cornerstones of digital audio and are actually distinctly different but interrelated processes which work to covert music from an analog signal into a series of numbers.
The analog signal that represents music exists as a voltage that varies over time. The faster the signal varies over time, the higher the audio signal's frequency, (this is represented as "time information"). The greater the amplitude of the signal, the louder the signal is. Sampling and quantization is the process of producing a series of binary numbers, called "words," that represent the analog waveform. An A/D converter encodes the signal's time information by sampling the analog audio signal at discreet time intervals and assigning a numerical value to this information. The amplitude information is encoded by generating a number that represents the analog waveform's amplitude.
The combination of this "time information" and the amplitude information is stored as a binary word in the digital realm. Thus, when the binary words are converted back into voltages, the analog audio waveform is roughly reproduced.
Quantization is the most important factor of the A/D conversion process that allows an engineer to digitally maximize and compress the audio signal. It has to be remembered that quantization is simply the generation of a binary number that represents an analog waveform's amplitude. In other words, the binary number that is generated through the process of quantization is a digital representation of the audio signal's analog voltage when the sample is taken. It is easy for an engineer to increase the binary number that represents voltage, thus increasing the amplitude of the audio signal. This process is called "digital maximazation." The process of adding a like amount of digital amplitude information to the entire digital sample (a song for instance) is called "digital compression." By subjecting a digital sample of recorded music to the interrelated process of digital maximazation and digital compression, an engineer ends up with a louder piece of recoded music that plays loud all the way through. This final product is now suitable for radio playback because the artist will now have the loudest song on the radio.
The only problem with the final product is that now the music doesn't have a natural waveform. A sine wave should roll naturally, with nice round tops and bottoms. Through the process of digital maximazation and digital compression, the engineer creates a waveform that is clipped at the peaks (top and bottom) and our ears perceive this clipping as distortion. This is the reason that most "older people" find new music irritating and they get tired listening to new music real quickly. It is not necessarily the music itself that is irritating them, it is the way it is reproduced.
So there you go. This is the story of digital maximazation and digital compression. Even though an audiophile has invested a great amount of time and money into their system, a new CD will still sound terrible simply because of the distorted waveforms that we are reproducing through our systems.
Rocky Bennett
Post edited by therockman on
Comments
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I think we have another rocket scientist amongst ourselves.
Good job rock but you forgot to mention 1 of my hero's... Mr. Nyquist.
HBomb***WAREMTAE*** -
Nah, I think the new music just sucks otherwise why would so many of my CD reissues sound so good?
And Henry, my hero is Mr. Nyquil...More later,
Tour...
Vox Copuli
Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb
"Death doesn't come with a Uhaul." - Dennis Gardner
"It's easy to get lost in price vs performance vs ego vs illusion." - doro
"There is a certain entertainment value in ripping the occaisonal (sic) buttmunch..." - TroyD -
Somehow I do agree with you Tour2ma, but this story is a work in progress. I do like some new stuff though, Norah Jones for example. But let me finish my story, and maybe I will include Mr. Nyquist and his wonderful therom.Rocky Bennett
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It's actually A/D (analog to digital) converters doing the first process
D/A is the other way around. And yes, it does matter as there are two kinds of converters.
A lot of the new music sounds like crap because they master is very hot and loud on the CDs. Most of population have crap for systems, and they want their music to be loud, not accurate. It's unfortunate.LSi 9/C/FX
Arcam AVR-200 -
Of course you are right Steve, and the appropriate changes have been made in my post. I do appreciate your input, and like I said, this little story may get some more posts by me and others to clarify and expand on its theme, if there is enough positive feedback like yours.Rocky Bennett
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I kinda have a problem saying that CDs sound like crap. I've listened to records (was a DJ) and they have a unique sound, I wouldn't say it's better, but it's more unique. I had a pretty decent setup as well, so I can't really say it was the equipment.
I've got some CDs that sound phenomenal, but I have a couple that were mastered too loud.
I think SACD and DVD-A will solve most problems LSi 9/C/FX
Arcam AVR-200 -
Well Steve, it seems that you are my biggest critic on this thread, which is just fine. This thread is a work in progress, which means that all feedback and ideas are certainly welcome. Actually my original intent in posting this ramble of ideas, which I really did research before I wrote it, was to open a dialog.
But to address your latest concern. I did not mean to imply that all CDs sounded loud and distorted, but there has been a trend that makes more and more of the popular CDs sound bad. You are right in pointing out that many CDs do indeed sound good. My AC/DC remasters sound fantastic, as does the Madonna remasters. But these discs are very well done with a lot of attention to detail. On the other hand, the ESSENTIAL STEVIE RAY VAUGHN sounded terrible as did the MARTIN SCORSESES JIMI HENDRIX BLUES disc. So it is a matter of the producers intent, and not the technology. The Cd based PCM encodig technology is actually fine when applied properly, and you are correct in pointing out that SACD and DVD-A are really fantastic. Actually, my collecting and enjoyment is dominated by SACDs at this time, both 2 channel and multi-channel.Rocky Bennett -
Well, rock on then... man...
There are a lot of ways to screw up digital technology. More steps in the process yeild more opportunities to fail.
In the beginning it was rushing so fast to make CD's that masters with the RIAA equalization still in place were used. And as of late it's pushing the recording level to hard. But when it's done right, it can be very satisfying.
The first couple years I owned a CDP, the only discs I bought were classical (except DSOTM, which was an obligatory buy). Why only classical? Dynamic range and playback time... but I digress...
So keep going... I want to see your musings on sampling rate and other digital delights...More later,
Tour...
Vox Copuli
Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb
"Death doesn't come with a Uhaul." - Dennis Gardner
"It's easy to get lost in price vs performance vs ego vs illusion." - doro
"There is a certain entertainment value in ripping the occaisonal (sic) buttmunch..." - TroyD -
Not that I have any major knowledge in this subject but have common comments on the matter.
Ever heard "the better the equipment, the worse the music sounds?". Boy did I go through that. Most of the late 80's and 90's rock I have on CD just plain stink as far as sound quality goes, after I got the current system up and going. Before B&K it didn't "hurt" to listen to these CD's. Now they stay in the basement. I can't stand to listen to them on the main system. Extremely harsh are the best two words I can describe for them. I talked with a friend of mine at work about this a couple of years ago and he stated the words digital compression. First time I ever heard this about CD's but he said that many companies have been using this for a while now.
Some CD's are better than others but wow, what a night/day difference.
As far as the new music, rock or boppy top 40 stuff, out there I don't like it anyway. This is one reason I think there is much interest in the older music, esp. 70's and early 80's, and yes, even country/western (which I do like BTW). As a matter of fact TOTO IV sounds better than almost any other CD I have concerning this. Not including what of what I mostly buy now, classical and jazz/piano (Telarc).
I will continue to read this thread with interest, thanks for the insight!Remember, when you're running from something, you're running to something...-me -
Just a tad off topic,
Has anyone thought to listen to Eminem on a good system?
Ear plugs please?
I like new rock. But for all thats holy, I need a treble control of -200! Very harsh, compressed, no excuse bad highs! I throw in one of my moms' old CDs'. Soundstage is so spread out, I can actually tell where the snare begins and the singers head starts. Oh well. This is one reason the music industry does so poor, that and the music now just SUCKS.- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit. -
Good call Sid. Music nowadays could just plain SUCK on any system out there. I haven't listened to anything new, as in the last 4 -5 years of new music, on CD....Remember, when you're running from something, you're running to something...-me
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Uh huh ... In more ways than one ...Originally posted by Vr3MxStyler2k3
the music now just SUCKS. -
Originally posted by smglbrth
Good call Sid. Music nowadays could just plain SUCK on any system out there. I haven't listened to anything new, as in the last 4 -5 years of new music, on CD....
Depends on what you are looking for. I've bought MANY CDs in the last few years that have sounded phenomenal.
It basically boils down to what the record company wants to hear, and WHERE they think the primary listeners are going to listen (car, boombox, club, etc).
I've found like a lot of Trip-Hop, Downtempo, Acid Jazz, Ambient, and most techno (not top 40 dance) are recorded VERY well. At least, in my experience.LSi 9/C/FX
Arcam AVR-200 -
Originally posted by Vr3MxStyler2k3
Just a tad off topic,
Has anyone thought to listen to Eminem on a good system?
Ear plugs please?
I like new rock. But for all thats holy, I need a treble control of -200! Very harsh, compressed, no excuse bad highs!
I'm gonna go along with Sid on this one. The first time I listened to Eminem on my system I was really suprised by just how terrible a recording could be. -
Originally posted by Steve@3dai
It basically boils down to what the record company wants to hear, and WHERE they think the primary listeners are going to listen (car, boombox, club, etc).
I agree with Steve about the way that recorded music sounding is a decision of some record company executives. I bought two brand new releases a couple of weeks ago; Courtney Love's brand new one, AMERICA'S SWEETHEART and Norah Jones new one, FEELS LIKE HOME. The difference in sound quality between these two CDs is phenomenal, yet both were released on the same day. The Norah Jones disc sounds great, real ambiance and natural timbre, no overly heavy mixing or loud passages. But the Courney Love Cd sounds "hot" from the beginning to the end, with a lot of distortion and compressed passages. It is a matter of what the record companies perceived as their core audience, and what they though the people wanted to hear.
My next chapter in this ongoing saga will deal with the Nyquist theorem, and the limits in redbook CD quality sound (i6 bit/44.1 khz) and DVD-A sound quality (which can extend to 24 bit/ 192 khz) differ. I might also have time to discuss the debate surrounding DSD sound technology as used in SACDs.Rocky Bennett -
