O.T. > CD-R’s

As far as I can tell, there are only two types of recordable CDs, widely available: CD-R and Audio CD-R. The Picture CD you’re referring is probably only a CD-R which has a better life span than regular CDs. On the Memorex site, it says it comes with a software to edit picture. So I’d say it’s a regular CD-R.

Just for the record, Audio CD-R are used in the home CD recorders, units you can connect to an amplifier (not a computer). I have a NAD CD recorder at home and it cannot use regular CD-R / CD-RWs, only those specially identified "Audio CD-R / RW" (of course, they’re more expensive!)

Memorex link : http://www.memorex.com/products/category_display.php?cid=159

Ray

Thanks Ray, I really didn’t think there was a difference. Note to self; buy discs !

"Ray" wrote in message

Just for the record, Audio CD-R are used in the home CD recorders, units

you can connect to an

amplifier (not a computer). I have a NAD CD recorder at home and it

cannot use regular CD-R /

CD-RWs, only those specially identified "Audio CD-R / RW" (of course,

they’re more expensive!)

And as far as I know, there’s not any physical difference. The only difference is that some sort of serial number on the "audio" discs identify it as such. The "audio" discs cost more, because the RIAA managed to get a per-disc royalty tacked onto the price of the blanks, which they of course enforce by requiring the home stereo burning equipment to check for the "audio" discs specifically.

Pete

And as far as I know, there’s not any physical difference.

Actually, "audio" discs also have a little extra headroom that is necessary to make them run in first generation cd players–not an issue unless you still have a cd player from the first five years or so after they were invented.

Barbara,

"audio" discs also have a little extra headroom

That’s very interesting. What’s "headroom?" Is is unused space at the outside edge of the disk?
Bert

It’s actually unused space at the top and bottom of the frequency bands. The early cds were created on the assumption that since you can’t consciously hear those frequencies they are just wasted space, so they just chopped off the the top and bottom to allow longer recording time, which is one reason why so many early cds, especially of classical music, sound so one-dimensional.

Anyway, really, really old cd players don’t know what to do if they find data in those zones, so "audio" cds have a sort of buffer zone there to fake the void the old players look for.

"Barbara Brundage" wrote in message

It’s actually unused space at the top and bottom of the frequency bands. The early cds were created on the assumption that since you can’t consciously hear those frequencies they are just wasted space, so they just chopped off the the top and bottom to allow longer recording time, which is one reason why so many early cds, especially of classical music, sound so one-dimensional.

Audio CD’s store 8-bit bytes, just like regular CD’s. The audio data is represented as a series of pairs of 16-bit samples, 44100 of these pairs for each second of audio.

Frequency data is implicitly stored, in the waveform represented by the actual data on the CD. There is no "headroom" in the sense in which you describe. Digitally encoded audio can always represent, with complete accuracy, arbitrarily low frequencies (down to 0 Hz), and the upper limit is determined not by the data stored (which is just a sequence of samples) but the rate at which that data is to be played back (called the sampling rate, and with CD’s that rate is 44.1Khz, as mentioned above).

The maximum frequency that can be represented by the 44.1 Khz sampling rate for CD’s is 22.05 Khz, in theory. In reality, it’s a little less, but in any case, there’s not any physical difference that could exist between two CD formats that could make any difference with respect to the range of frequencies that can be recorded.

A Google search on "Nyquist" will turn up a bunch of interesting links on this topic.

By the way, the size of the audio samples (16-bits for audio CD’s) affects the signal-to-noise ratio. An approximation used in digital audio theory is that you get 6 dB of signal-to-noise for each bit of data per sample. So CD’s get, in theory, 96 dB of signal-to-noise.

My apologies in advance if this post seems confrontational. Just trying to get the facts straight, that’s all.

Pete

Hi, Pete. Might want to have a chat with a recording engineer or two. They would disagree, at least in every studio I’ve ever been in. 8^)

Barbara,
When I read your post #6, I was really confused, because, as an engineer and a music fan, I understand the CD data format and the Nyquist criteria for data sampling. I have owned a CD player since they first came out. In fact, I was composing a response in my head when I read Peter’s post.
Like Peter, I do not mean to confront you, but his excellent tutorial on digital recording theory is correct, as far as I know.
If you could find a website or give us a reference to what you are talking about, I think we both would appreciate it.
Bert

Gee, Bert, I was just going on what studio engineers have always told me. As I say, perhaps y’all are correct; it’s just different from what I’ve always been told in the recording studio. Could be–there are always myths wherever you go.

"Barbara Brundage" wrote in message

Hi, Pete. Might want to have a chat with a recording
engineer or two. They would disagree, at least in every
studio I’ve ever been in. 8^)

Perhaps you misunderstood what they were saying.

During recording, the engineer does need to be careful about the audio levels (amplitude, not frequency) to make sure that the volume does not exceed the resolution of the digital data (known as "clipping", which is very similar to the analog version of "clipping"). In theory, they could go right up to the maximum levels afforded by the 16-bit sample, but in reality, low-end CD players sometimes don’t reproduce such "maximum volume" samples correctly (their analog components clip, and can’t reproduce the full spectrum that the digital sample can represent).

The fact that this difference between maximum levels in the recorded audio and the maximum level theoretically capable of being reproduced is called "headroom" makes me think that this may be where your misunderstanding comes from.

To bring this back to the topic of this forum, this effect is very much like when you have bright areas in an image and you can’t tell the difference between two pixels that are not actually the same color. In the visual realm, this usually happens when capturing the image, but it could happen at any step along the way, including the video card or monitor.

In the audio realm, the effect causes kind of a "scratchy" noise to come through the speakers. In the visual realm, you just see a lot of white. If the problem is at the monitor, often just turning the brightness down on the monitor will let you see the difference in pixels, just as turning down the volume on your stereo will make the noise go away if the clipping is happening in the amplifier (as opposed to being in the original audio source).

For more that you ever wanted to know about CD-R, look here: http://www.cdrfaq.org/faq07.html#S7-17

That link will actually take you directly to the discussion regarding CD-R blanks, but the web site in general is chock full of all sorts of information about CD-R that most people never need to know. 🙂

Pete

Perhaps you misunderstood what they were saying

Sure, if that makes you happy. Whatever.