What's the native bit rate of PAL NICAM stereo audio?

[ajmoss]

I need to record a TV programme in order to make two copies of it: one in VCD format, the other in a low bit rate DVD format (probably 3.0Mbps at 352x572 pixels). These two formats have different audio bit rates.

I'll be recording a NICAM signal, and rather than recording it twice, I'd rather capture in 352x576 MPEG-2 and use TMPGEnc to produce the VCD format disk.

Should I capture the audio at 44.1kHz or 48.0kHz? Obviously it will need to be converted once, but I want to avoid further quality losses that would be caused by recording it in the "wrong" format (which involves converting the bit rate on the fly) and converting it back again.

[jggimi]

Hmmm... here's Hakko504's description:

http://forum.doom9.org/showthread.php?s=&postid=84029

I hope it helps.

But if your card converts the audio, it really doesn't matter. (I don't know, since we don't have NICAM cards in this part of the world.)

I'd capture in Linear PCM, and I'd probably go with a sampling rate of 48KHz, then downsample for the VCD when converting to MP2.

I'd probably want to keep the audio in PCM form for the DVD, if I was going for maximum quality.

[ajmoss]

Thanks for that. I'm rather bandwidth-limited, in that I need to fit nine 50-minute programmes on two or three DVD+RWs.

I was wondering why most of the capture options on my video card software (which default to 224kbps MP2) run at 44.1kHz; only the options that are specifically designed for DVD mastering capture at 48kHz.

The post you quote gave the sample rate of NICAM audio as 22.05kHz. 44.1kHz is nicely an integer multiple of this frequency.

[erratic]

"All You Ever Wanted to Know About NICAM but were Afraid to Ask" (http://www.qsl.net/zl1vfo/nicam.htm)
In fact it's more than I ever wanted to know about Nicam, so I didn't bother to read it. ;)

[tedkunich]

If you are "Capturing" i.e. Analog capture vs capturing via a transport stream, what the original signal was transmitted/digitized at is irrelavent - the reciever reconstructs the original audio and your capture card only "sees" an analog source. If this is the case, capture the audio at 48Khz for your DVD project and then re-encode the audio later and downsample to 44kHz for the VCD project. If you are indeed capturing a transport stream, I'd doubt that there are many tools that will handle the decompression.


T