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SACD Question

 

Bronze Member
Username: Rickypearson

Post Number: 46
Registered: May-04
Hey GUys Do u think you could tell me what a SACD is and what advantages they Have or cds Thanks!!
 

Gold Member
Username: John_a

Post Number: 2130
Registered: Dec-03
Super Audio Compact Disc. Advantage to consumer: Greater detail, better sound. Advantage to industry: something to boost flagging CD sales; copy protection - you cannot "rip" files.

See also Twilight of the Compact Disc.
 

Silver Member
Username: Arnold_layne

MadridSpain

Post Number: 137
Registered: Jun-04
SACD is a "new" technology for digitalizing, here's a basic comparision:

CD: Sound pressure is represented by 16 bit number (0 - 2^15), 44.100 times per second.

SACD: 1 bit indicates if sound pressure goes up or down, 2.822.400 times per second.

Hence, SACD can provide a much more precise digital representation. IMO a noticeable improvement for vocals and acoustic instruments, sounding more natural.

Also, SACD can be 5.1 surround. This means more details in complex music.

Cheers
AL

 

Silver Member
Username: Myrantz

Post Number: 694
Registered: Aug-04
Arnold is right, SACD recordings are in stereo or stereo/multi-channel, and the hybrid discs have a 'CD' layer also enabling playback on a standard cd player.

IMO, Super Audio Cd's and DVD-Audio are a very postive step on the road to perfect audio sound.
 

J. Vigne
Unregistered guest


Arnold - If sound pressure is the only item measured and therefor repesented how do we know what frequency(s) are on the original?



 

Silver Member
Username: Arnold_layne

MadridSpain

Post Number: 138
Registered: Jun-04
To be precise, I should say "air pressure". Sound is pulses/contractions of air reaching our ears, the result of horisontal push-pull movements of speaker membrane (or whatever source). The magnitude of these air pressure changes determines how strong is the sound. The amount of pulses per time unit determines the sound frequency, i.e. high or low tone.

So PCM is roughly about representing current air pressure by a binary number (more bits => increased precision is possible) at a certain sample frequency (more sample KHz => higher sound KHz can be represented).

DSD (SACD technology) represent unitary changes (up or down 1 unit) of air pressure. Basically doing the same job as PCM, but DSD does not consider whether the air pressure change is small or large. Therefore sample rate must be very high, so that a large change can be represented by many small changes.

Cheers
AL
 

J. Vigne
Unregistered guest


Wow, I've never seen anyone try to describe DSD in only three sentences.

So, if you're saying "air pressure" (are we talking P.S.I.?) represents frequency, I still don't see, in your description, what measures "sound pressure" or amplitude of a frequency. Sorry, just trying to clarify.



 

Silver Member
Username: Arnold_layne

MadridSpain

Post Number: 141
Registered: Jun-04
Actually, I think the air is moving back and forth, so we have maximum and minimum pressure levels. The concepts are then:

- Frequency is how often maximum pressure is reached.
- Amplitude is the difference between maximum and minimum pressure.

It is easier to visualize if the horizontal air movements are transposed into a curve diagram of air pressure (vertical axis) over time (horizontal axis). Just as the common picture of a sine wave, which in acoustics is no more, no less than a pure tone.

Digital representation is about plotting this curve. PCM describes the vertical position at each instant of time (how high is pressure). DSD on the other hand just tells if the position is higher or lower than at the previous instant of time (pressure change).

It is also important to differ air pressure change frequency (how often there are pressure peaks)from digital sample frequency (how often pressure is measured).

Cheers
AL
 

Silver Member
Username: Arnold_layne

MadridSpain

Post Number: 142
Registered: Jun-04
Just a couple of precisions:

"Sound pressure" is formally used as a measure of energy (air pressure) arriving to a surface.

"Air pressure" is in this context relative to static atmospherical pressure.
 

Bronze Member
Username: Bleustar

Pensacola, Florida

Post Number: 97
Registered: Jul-04
Thanks Arnold for the lesson. I love reading about this in a way that is not so (text book).
 

Silver Member
Username: Arnold_layne

MadridSpain

Post Number: 145
Registered: Jun-04
No problemo - the more we all learn about these issues, the better we understand why CD was just a step on the way.

Another way to answer the original question (Ricky, are you still there?) is to measure and describe how the different formats actually sound. There is a lady who has performed some interesting "spectral and dynamics comparision":

http://users.bigpond.net.au/christie/articles.html

Heavy duty because of her cientific approach, but IMO worthwile read trough to see the conclusions.

Cheers
AL
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