|
For the CD: WHY 75 Frames/second???
|
View this Thread in Original format
| ali92 |
| I always wondered this. Wouldn't a nice, round number like 100 be better? Or a traditional 30 FPS, like video formats? It's a pain making a CUE file if you have to convert between milliseconds and CD-frames becaue you're using a sound editor that doesn't display the time in MM:SS:FF (CD) format. Instead, it is displayed in MM:SS:XYZ (XYZ is a decimal number showing thousandths of a second, or milliseconds). If CDs used 100 frames per second, it's easy making a CUE file because you can round up or down the last value (Z) to get an appropriate value. If they used 30 frames per second, most sound editors that display times in MM:SS:FF format will work fine. |
|
|
| trancaholic |
| What do you mean by CDs having 75 frames per second? As far as I know Audio CDs are not divided into frames, but are measured in bits/second (usually 44)?!? |
|
|
| ali92 |
| quote: | Originally posted by trancaholic
What do you mean by CDs having 75 frames per second? As far as I know Audio CDs are not divided into frames, but are measured in bits/second (usually 44)?!? |
You're talking about Sampling Rate. That's 44100 Hz. I'm talking about measureing time values below 1 second, like Hundreth-seconds but, in the CD's case, when you measure time BETWEEN seconds, there are 75 FRAMES that make up each second. Each frame in CD-DA is equal to 2352 bytes. http://www.cdrfaq.com/ has more info. Also, in DATA, they're called "sectors". Those are 2048 bytes each, the rest of the bytes go to headers and other info required for Data files to be stored on CD, as well as error-correction. In CD-Audio, those same sectors are called Frames and Audio needs NO headers and there is way less error-correction. |
|
|
| drizzt81 |
| quote: | Originally posted by ali92
You're talking about Sampling Rate. That's 44100 Hz. I'm talking about measureing time values below 1 second, like Hundreth-seconds but, in the CD's case, when you measure time BETWEEN seconds, there are 75 FRAMES that make up each second. Each frame in CD-DA is equal to 2352 bytes. http://www.cdrfaq.com/ has more info. Also, in DATA, they're called "sectors". Those are 2048 bytes each, the rest of the bytes go to headers and other info required for Data files to be stored on CD, as well as error-correction. In CD-Audio, those same sectors are called Frames and Audio needs NO headers and there is way less error-correction. |
you did just answer your own question did you not?
if you are wondering why it is 44.1kHz (which appears to be to be the reason for the 75 FPS) is that we can hear -reasonably well- till up to 20kHz and the sampling theorem suggests that you can 'perfectly reproduce' a signal if you sample it at twice the highest frequency... |
|
|
| ali92 |
| quote: | Originally posted by drizzt81
you did just answer your own question did you not?
if you are wondering why it is 44.1kHz (which appears to be to be the reason for the 75 FPS) is that we can hear -reasonably well- till up to 20kHz and the sampling theorem suggests that you can 'perfectly reproduce' a signal if you sample it at twice the highest frequency... |
I didn't just answer my own question. As I said before I wanted to know why was 75 used instead of 100. THAT'S ALL. I didn't mention a WORD about 44100 or Sampling Rate in the original question. I guess this discussion has come to a close... |
|
|
| drizzt81 |
here is an idea:
44100 / 75 = 588 (still confused, right?)
2352 / 588 = 4 (<< looky here, an integer!!!)
they used 75 so that they can fit 4 frames/sector..
or am I misunderstanding something here?
sorry, i am just randomly playing around with the numbers, seeing that it is 4 AM here :D
[edit]
probably did it for the same reason that EE's decided that ATM cells (network technology) need to be 53Bytes is size..[/edit] |
|
|
| ali92 |
| quote: | Originally posted by drizzt81
here is an idea:
44100 / 75 = 588 (still confused, right?)
2352 / 588 = 4 (<< looky here, an integer!!!)
they used 75 so that they can fit 4 frames/sector..
or am I misunderstanding something here?
sorry, i am just randomly playing around with the numbers, seeing that it is 4 AM here :D
[edit]
probably did it for the same reason that EE's decided that ATM cells (network technology) need to be 53Bytes is size..[/edit] |
OK, now I understand... Thanks! |
|
|
|
|
