What's wrong with SACD, and how to fix it

You don't need to sum bass frequencies when cutting vinyl!! Listen to the Mercury Living Presence vinyl of Howard Hanson's Nordic symphony. The bass drum is incredibly strong (and well recorded) and it predominates in the left channel. It shakes the whole room!!

 

Real quick Nyquist sampling lesson:

1) Any sine wave can be represented by sampling two points in that sine wave.

2) That sine wave can then be recreated by using those two sampled points as reference points.

This is pure math--no grey areas here.

Anyway.........

3) As far as the information between the sampling points: if this information--which will also be in the form of a since wave--is not of a frequency outside the format's operating range (20kHz for CD, 44kHz for 96kHz/24bit PCM, etc) that wave will ALSO be correctly sampled. It won't be lost or thrown out. Even there is a quick/random transient, if its frequency is at or under 20kHz, 44kHz, etc it will also be sampled.

4) The quality of the DAC's analog circuitry--which actually generates the music you hear--is now what will determine how accurate the recreated sine wave will be. And sine waves are not difficult to recreate.

Remember, no matter how complicated a musical waveform looks, all those bumps & wiggles you see are individual sine waves--they are simply superimposed on top of each other. But a digital encoder can "see" the individual waves, as long as its sampling rate is high enough.

 

This is not true, my understanding is that you Do have to sum the bass frequencies for vinyl cutting. Read the article in the new the absolute sound written by Jonathan Valin about the bass on the SACDs of the new RCA living Stereo recordings compared to the same recording on vinyl. Much more bass presence on the SACDs.

 

You don't have to sum the bass when vinyl cutting, but there are technical reasons it has been traditionally done.

 

According to my last exam, I can only hear up to 18 KHz. The CD brickwall filter goes up to 22 KHz... so I wouldn't be able to listen to anything higher than that range, anyway.

Yep, but thankfully, due to the way low pass filtering works, recreating it is very simple, actually.

 

Two points:

1. DSD does not use brickwall filters which is an improvement over PCM.

2. I don't think the case is strong for DSD throwing away too much in between samples...while this is technically true with all digital audio, in DSD the sampling rate is so fast that I hear many transients which I believe contributes to a more natural, analog-like sound. If DSD was sampling at 5.8mhz then it would be even better but as long as the transients are captured then the recording sounds good to me.

I have A/Bed high end SACD players and $10K turntables and the turntable always wins although it is slight against Meitner DSD DACs...but the convenience is real over analog. Of course, many audiophiles like the tweaking aspects of vinyl.

 

Oh boy, here we go again. Folks we have been through this a number of times on this forum. So one more time I will try to explain.

My Credentials: Ph. D. Physicist

My Experience: Now work for a major computer corporation, use to work for a major petroleum corporation where I digitally recorded (on tape) analog data that cover the frequency range of 20 Hz to 20 KHz (gosh, does that remind of another frequency range )

Joe is 100% right, analog is the ultimate in hi-rez, it is what all digital techniques try to imitate. Analog is like digitizing at an infinite sampling frequency with an infinite number of bits, you cannot do better than that. Does analog have band with limitations- of course it does. Does anyone know of an amplifier, a tape machine or any other analog recording device that has an infinite bandwidth? But, by in large the bandwidth limitations in analog are less sever than they are in digital.

Now as to Nyquist who was a mathematical genius and one of the true fathers of digital data acquisition and manipulation (along with Fouier - as they use to say in my physics text, it is left as an exercise to the reader to find out what Fourier has to do with all of this ). Nyquist proved mathematically that as long as you sampled a bandwidth limited signal at twice the frequency of the bandwidth limit the digital data can exactly reproduce the bandwidth limited signal. There are other threads in this forum that show what a CD band width limited signal of a square wave or an impulse signal look like. They do NOT look like the real thing. It is true that an infinite combination of sine waves can form any musical signal but no digital technique that exist today gives you an infinite combination. It does not matter if you can hear to 18KHz or only 12KHz as I can at my old age, the bandwidth limitation effect the fundamental signal and you can hear it.

I hope this helps.

 

I'm not sure why this square wave and digital thing keeps popping up--I have never seen an oscilloscope trace of the analog output of a digital component playing music look even remotely like a square wave.

All this talk about infinite resolution in real world components is rather misleading--analog circuits have more chances to generate extraneous distortions that are added to the final signal than digital does (think about that signal passing through all those dozens of capacitors, resistors, transistors, PC board traces & individual wires passing near certain components, temperature-induced problems, etc). Luckily certain of these distortions do sound good but the fact remains that they are not part of the original signal & can also obscure some of the original signal's details. So theoretically analog has infinite resolution but in actual practice this never happens.

BTW: whenever I mention "digital" I'm only including PCM and not DSD. Personally speaking, I think DSD is.....doing something......to the signals it handles to produce a certain sound. I.e. I think it is not more accurate than the PCM system but actually less accurate. Again, just my opinion.

So if someone likes the sound of analog that's great--no argument from me. But to say it's the most accurate way to convey a musical signal is very debatable.

And generally speaking, since digital can convey signals more accurately, the format also has the unfortunate side effect of revealing deficiencies in other parts of the signal chain that many analog systems cannot. So engineers have to be more careful in their choice of signal chain components than with an all-analog system which generally can hide more of these problems because of its inherent deficiencies. I think this is why master tapes of classic albums heard through a digital medium can sound different than their LP equivalent because we are now hearing more deficiencies of the tape medium itself (& minus the problems of the vinyl format), and any mistakes the studio made regarding EQ, compression, etc. So I think that's why so many people think the digital version sounds worse than the vinyl version, because vinyl's "good-sound frosting" is no longer there to smooth over those problems.

And when I say "deficiencies" I only mean that in a relative way--obviously, analog recordings can sound excellent so IMO really all we are arguing about are mostly academic differences, which is why I don't mention this stuff very much since it takes the fun out of this hobby for me.

What music contains square waves? None that I know of, unless a synthesizer is used and square waves sound really nasty & definitely not musical.

Impulse response? Is this one of those "tests" we've all seen before involving another format that used an impulse on an unmarked graph at some unrealistic frequency like 80khz or something similar?

And correct me if I'm wrong but don't most mics used by recording studios today trail off by 20kHz? And quite a few of those vintage mics in vogue today barely make it to 15kHz. And, can any of these mics respond to those impulse signals mentioned above?

I know there is a still a debate going on about whether frequncies past 20kHz actually contribute in some unknown fashion to overall musical realism but for me anyway, until solid proof of this phenomenom is found, I'm not going to obsess over what might/could/probably be as far as improved musical fildelity.

 

It was really not my intention to start an analog vs digital debate. But I can't let all this misinformation pass. "Analog is like digitizing at an infinite sampling frequency"? No, it is like digitizing at a finite sampling frequency, because as you contradictorily say later bandwidth is always finite. "Infinite number of bits"? No. If an analog tape recorder has an SNR of 72dB, for example, that is like 12 bits. 12 is not infinity.

Finally, we have this stuff about "square wave". Contrary to what you assert, if you limit the bandwidth of a square wave to the human hearing range, the sound does not change. Or if it does, it's because of distortion in your speakers, in which case filtering out the high frequencies is an improvement in the sound.

Microphones don't pass square waves, speakers can't reproduce square waves, and you can't hear square waves. Audio devices, whether analog or digital, are designed around what we can hear, not what we can't hear.

 

Taurus and Luke, I am really sorry if I upset you. I would really help if I understood your back grounds, have you ever had formal education in integral transforms which is what digitization really is. Luke you are confusing quantization noise and sytem noise. Taurus, Impulse signals are every where in real music, study some of the other threads on this and see what digitization does. DSD is absolutely on the right track, some day when we can use DSD sampling rates at 24 or 30 bits digital will sound analog, but the technology is not there yet. Twenty+ years ago I gave up bits (I used only 8 bits) to sample at higher frequencies, it made a huge difference. (Sadly the scientist who taught me this died a year later.) If you want to learn more on this PM me and I will send you some links, suggest some reading material and then we can talk one on one. I will be very busy for the next week or two but around the holidays I should have some time.

 

I'm not a physicist but I have worked on dozens of audiophile records and I do know this: 44khz sampling is not enough to capture transients within the 20hz-20khz band like 24/96 (especially 24/192) and DSD can. This is generally accepted as fact in the pro recording community.

I also think it is important to keep in mind that audio researchers have discovered that ultrasonic frequencies can affect what happens in the 20-20k range.

Having said all that nothing beats analog which is how we hear and the goal of digital as others have said. I think DSD gets close but with even higher sampling it would be closer.

 

I really feel that this debate is academic at best. Every link in the audio chain has it's inherent limitations, from the microphone at the beginning of the chain, to the cables and circuits throughout the chain, all the way to human ear at the end of the chain. I honestly think (from my limited understanding of physics which is way beyond the normal Joe Six Packs understanding of physics) that if we lived in a science-fiction world where we could design and build the ultimate high fidelity sound reproduction system, then analog would be the best and most accurate reproduction medium simply because, as has been pointed out already, natural sound waves are analog in nature. In the real world we understand the limitations of analog, such as the physical movement of needles on record surfaces and the physical size and unfortunate fragility of most analog playback medium, so our goal is to reproduce the natural sound waves in a digital medium that is as faithful as possible. There are limitations to every medium, there are flaws and sonic signatures to every link in the audio playback chain, but as human beings we should be wise enough to choose our own priorities and decide which medium best fits our needs, (i.e., convience, durabitlity, faithfulness and other factors to numerous to mention). Even though I don't have a Ph.D in physics, I feel that everybody on this forum is wise enough to choose the medium that fits their individual needs, and to argue with everybody else why their choosen medium is obviously the best. I have choosen digital even though I understand its limitations, I have personally choosen convience over whatever special qualities that analog offers. Thus, my stand is that digital is the best when done right.

 

I'm sorry, but sound waves are not 'analogue' in nature. It is is almost an oxymoron to say as such, IMO. Sound waves are created by a disturbance in the air which cause air molecules to 'shift' if you will. Our ears then detect the changes in the air pressure, send this information to our brain which interprets this as 'sound'. Actually, some might argue that how we hear is actually more digital in nature as it takes the brain to allow us to process something as sound, and the brain works with a complex logic not as an 'analogue' if you will. Sound waves are not analogue, they are what they are; what is analogue is all the things that seek to artificially capture and reproduce sound waves in an analogous fashion, and that is both 'digital' and 'analogue' recording techniques.

All of the debate about resolution etc. cannot be had without including the ultimate determining factor and that is the ability and limitations of the actual playback equipment and mediums to reproduce these sounds and how they affect the sound.

 

According to my dictionary (American Heritage, Fourth Edition, Copyright 2000), the definition of "analouge" is:

"Something that bears an analogy to something else. Of, relating to, or being a device in which data are represented by continuously variable quantities such as length, width, voltage or pressure."


Utilizing both of the above definitions of analouge, then sound in nature is absolutely analouge. What our brains do with sound is another thing altogether.

 

GoldenBoy, You are headed in the right direction but you need to get your definitions straight. Acoustics, the propagation of pressure waves through a media (solid, liquid or gas) is an analog phenomenon - it is not digital in anyway. How a coherent pressure change can propogate through a gas composed of molecules in somewhat random motion is explained in the area of physics called Statistical Mechanics and it is much too complicated to explain here. I took a year of Stat Mech in graduate school and it was one of the most grueling courses of my education, please trust me when I tell you that ordinary analog wave equations work just fine to describe sound waves in air. How the human ear and ear cannal work to capture the sound pressure change and convert it into an electrical signal that is received by the brain is also fairly well understood in medicine but I have no great understanding of it in detail. How the brain interprets those signals is a very active area of research, usually called psychoacoustics, and the scientific community is learning new things about how we "hear" all the time.

 

You're right tat analogue wave equations work fine to describe sound waves in air, otherwise so many people wouldn't be so fanatic about 'analogue' recordings, and , yes, all of this stuff really is too complicated to go into much detail about here. What I know is that even the most educated scientists, sound engineers, etc. cannot come to a consensus on what is the most accurate way to capture and recreate sound waves. What I take exception to (seemingly on a regular basis) is people claiming that sound is inherently analogue as a way to bolster a pro-analogue argument. Sound is sound, it is not 'analogous' to anything. If sound is analogue, the question then becomes what is it analogous to? Itself? Even in rockman's posted definition, he seemed to have overlooked two key words: 'device' and 'data'. As in "Of, relating to, or being a device in which data are represented by continuously variable quantities such as length, width, voltage or pressure."

There is nothing in that definition that says sound is inherently analogue. In fact, it supports an argument that even digital is 'analogue' in the strictest sense of the word as it uses a 'device' to store 'data' to 'represent' 'continuously variable quantities'.

 

Of course this is all academic, and we are not going to settle anything defintively here at this forum, but turning again to my dictionary it states that a device is:
"A technique or means."
Now the source of sound could be anything, a tree falling in the woods, a cannon being fired or a human voice singing. This is the source. The molecules in the air is the "device" that is conveying the sound from point 'A' to point'B'. These molecules are only the device, but they too have effects on the sound. The heavier the molecules (such as fog) the slower the air movement, the less dense the molecules (in a pressurized cabin for example) then the more sound pressure that is required to achieve a certain level of molecular excitement. But the air and molecules are only the "device" that exists in nature to convey sound waves from point 'A' to point 'B'. The word analouge now comes into play in the fact that when the sound wave is originally created this sound wave has a particular shape and size. It is this shape and size that needs to be communicated from point 'A' to point 'B'. Air movement is indeed an analouge device because the shape and size of the original sound is conveyed in a generally analougous manner. Of course, as was stated earlier, these analouge sound waves maybe transferred into a digital-like state in the human central nervous system, but is beyond the scope of this academic discussion.

 

It doesn't matter whether an audio recording is "analog" or "digital." We still hear them the exact same way - as a disturbance of air molecules (or however you want to define it). Digital is just the way the information is encoded and played back. Once the "sound" leaves the speakers it's all the same.

 

GoldenBoy, You are right and I now see what you meant. Sound is not analog it is just sound. In today's world analog has come to mean signal data that is recorded, processed, manipulated without digitization. That is what I meant when I said that ordinary wave equations work just fine to describe sound waves, there is no need to go digital. So, it looks like we all need to review our definitions. Good discussion.

 

Some thoughts on what has been discussed:

1) Of course wave equations explain sound waves and not digitallly encoded data. There is no such thing as an "analogue wave equation". Wave equations can be used to describe anything that can be considered to have wave properties. A bunch of numbers, while it may constitute the digital encoding of a waveform, does not itself have wave properties!

2) The last point in 1) is the key point in understanding the difference between digital and analogue information. A digitally stored waveform does not itself have wave properties but may be used to reconstruct the analogue waveform it encodes. An analogue stored representation of a waveform itself has the same wave properties as the original waveform except for any distortions introduced in the storage process.

3) The statement that sound itself is analogue is perfectly accurate. Imagine you are listening to someone playing a drum. The waveform carried within the air to your ear is an analogous representation of the displacements that the molecules of the skin on the drum were undergoing. Of course, sound waves don't have to travel through the air to be called sound waves. A sound wave, or more properly an acoustic wave, is simply a process whereby energy is tranferred from one place to another via an elastic medium. You can hear an analogous representation of a vibration via any number of processes. Suppose you are lying quietly in the bath and can hear your heartbeat. What your ear is picking up is acoustic waves within the water that are analogous to the movement of your chest due to your heart beating. How about Beethoven using a bone to transfer an analogy of the vibration of his piano strings to his skull via his teeth? What he is hearing are analogue representations of the original source of the vibration.



So, while I appreciate the attempts to distinguish both analogue and digital storage from "actual" sound itself it does not represent reality.

Analogue storage of sound waves is a fundamentally natural process.

The digital storage of soundwaves has no such fundamental relationship to the nature of sound itself.

I'm not saying digital storage cannot be used to produce fantastic sounding audio. Indeed, just becuse analogue storage if fundamentally natural, doesn't mean it can't produce horrible sounding results!


As for whether SACDs should contain a vinyl dub I would say definitely not. As others have said - if you like vinyl get a record player!!

 

Digital storage is just math. Digital storage IS based in natural law. So what if it doesn't occur naturally. Neither does that electric guitar Eric Clapton plays, or your Crown amp.

Gee, why can't we all just pick what we like and live with it instead of one trying to convince another that one's person's view is correct, while the other is wrong, or logic is flawed? You like vinyl and think vinyl playback is more accurate? Be my guest! You think digital is more accurate? Go ahead. This debate is realy pointless.

Do I want to stifflfe intelligent debate? No, but I can't see that anyone can win this one.

 

Grant,


you conveniently forgot to quote this bit:

"I'm not saying digital storage cannot be used to produce fantastic sounding audio. Indeed, just becuse analogue storage if fundamentally natural, doesn't mean it can't produce horrible sounding results!"

All I am trying to do with my previous post is to clarify the definitions of the terms "analogue" and "digital" as they relate to acoustic waves.

I always seem to get your goat in discussions involving analogue and digital and I can't quite figure out why!

Friends?

 

I know what YOU were talking about, and wasn't talking about you, or anyone else in particular, Malc! I just see this stuff as pointless.

Of course, we're cool!

 

I'm sorry, but, again, I cannot agree that sound is fundamentally 'analogue'. Sound is a natural occurrence, and whether an 'acoustic wave' as Malc S put it is in air or water or a solid mass such as stone, sound in its natural state is sound. Period. Without the medium, there is no sound. Without displacement of some sort, there is no sound. To put it more simply, the medium is the sound. A drum beating while suspended in a vacumm makes no sound. It is no more or less natural to make a record of that sound by carving a representation of it into shellac than it is to store it as binary code, which is mathematical and just as natural as air. As usual, IMHO.