Recording a live show from TV in LPCM mode

[PaulHarald]

Hi all, thanks for a great place for learning!

Have been wondering about this for a while: I have read several places that NICAM stereo is distributed as 728 kbps audio, so it's a bit more compressed than a CD which is 1440 kbps if I remember correctly.

My standalone DVD recorder (a Pioneer DVR-630) can record the audio as "high quality" LPCM mode which is a good thing for an audiophile wannabe like me. Better than the usual 256 kbps AC3 anyway.

But then: If I assume the audio is not compressed anywhere along the way from the source (which would probably be impossible to find out unless I email someone at the TV network in question) I guess I will have a DVD with LPCM audio which has been transcoded from the NICAM signal into LPCM.

Questions:

1) Is this OK to extract and convert to WAV -> FLAC and share here?

2) Am I right in the above description or have I missed something here?

http://www.answers.com/topic/nicam

http://encyclopedia.laborlawtalk.com/NICAM

I have no tool for frequency analysis (using a Mac here)...

(now just wondering why my share ratio is frozen. Is it because I have two Macs?)

[AAR.oner]

Audacity for audio analysis http://audacity.sourceforge.net/download/mac
MPEGInfo for DVD/video analysis [don't know where a link to this is anymore]

[Five]

1) yes, so long as the source has a 100% lossless pedigree. sometimes the audio can be captured as wav but the source was in fact lossy. check it with audacity ask for help if you want to learn how to do this.

2) I'm more of an audio specialist but your description sounds fine to me.

[PaulHarald]

Thanks people, I'm still learning. I have some more philosophical questions: My TV signal (regular cable TV, not digital TV) will, in all likelihood, have come from a digital source nonetheless, so I am in effect capturing a digital broadcast transitted in analogue.

I have learned that NICAM is 'digital', but as it is decoded at the user end, it is broadcast in analogue format, not digital - it only becomes 'digital' after it has been decoded by my TV and/or DVD recorder (thanks to Inabsentia at Dime).

So now my main question is this: How compressed is the audio at max in the lineage from cameras and mics to the TV set in my living room? In other words: The digital source, produced by the TV company, is probably better than 256kbps AC3. Or is it?

Like FM versus DAB: DAB is usually 128kbps but FM is not that compressed even if it was recorded digitally in the first place. If a radio station does a high bitrate digital audio recording, and air it on DAB radio it will be compressed to 128kbps along the way. Not good. When they air the same show on regular FM it's better, it's "FM compressed" but that's not that much.

So if we compare this to TV-land: Is a DIGITAL TV stream (audio) usually 256kbps? Or is it better? And for the non-digital TV with Nicam stereo: May the NICAM stereo signal be less compressed? In that case, the freq analysis of my LPCM audio capture would look better. Why would standalone recorders have the options of 384kbps AC3 and the best ones even LPCM - the user manual says "for recording uncompressed high quality audio..."

It would all boil down to how the TV network operates, and I guess there will be different answers from different countries etc. I think I'll do some freq analysis myself now, and check it out. And maybe even send an e-mail to NRK and SVT.

[ssamadhi97]

Originally Posted by PaulHarald

So if we compare this to TV-land: Is a DIGITAL TV stream (audio) usually 256kbps? Or is it better?

Setting aside the fact that 256kbps do not always equal 256kbps (see next paragraph), I see 192-256kbps MP2 here (Germany) most of the time.

Originally Posted by PaulHarald

And for the non-digital TV with Nicam stereo: May the NICAM stereo signal be less compressed? In that case, the freq analysis of my LPCM audio capture would look better.

Debatable. While the bitrate is significantly higher, compared to AC3 and MP2 NICAM also lacks (to the best of my knowledge) any advanced encoding tools like the ability to throw away inaudible data first based on a model of the human hearing, making it less efficient. On the whole it's probably still better, but it might not be as much as you expect.

Originally Posted by PaulHarald

Why would standalone recorders have the options of 384kbps AC3 and the best ones even LPCM - the user manual says "for recording uncompressed high quality audio..."

Because even if the source is already lossy, encoding it again sacrifices even more quality. So you want to be able to throw as much bitrate at it as possible.

[4candles]

Originally Posted by PaulHarald

I have learned that NICAM is 'digital', but as it is decoded at the user end, it is broadcast in analogue format, not digital - it only becomes 'digital' after it has been decoded by my TV and/or DVD recorder (thanks to Inabsentia at Dime).

I don't understand that sentence - NICAM is a digital broadcast method. The audio starts as analogue (maybe) in the TV studio, gets converted to NICAM (a digital format), the NICAM bitstream is transmitted with the analogue TV broadcast, and then finally your TV or VCR will convert the NICAM digital bitstream back to analogue audio.

More information that you probably want on NICAM can be found here:

http://tallyho.bc.nu/~steve/nicam.html

Basically, the NICAM process starts by sampling the audio at 14-bit/32KHz, and this is "companded" (a lossy data-reduction process) to 10-bit/32KHz for transmission.

So if we compare this to TV-land: Is a DIGITAL TV stream (audio) usually 256kbps? Or is it better? And for the non-digital TV with Nicam stereo: May the NICAM stereo signal be less compressed? In that case, the freq analysis of my LPCM audio capture would look better. Why would standalone recorders have the options of 384kbps AC3 and the best ones even LPCM - the user manual says "for recording uncompressed high quality audio..."

Most digital TV stations use 256kbps MP2 compression. Some use 192kbps or even as low as 128kbps, but I've never seen any TV (or radio) stations broadcasting MP2 audio greater than 256kbps.

Some TV stations have (sometimes in addition to MP2), a higher bitrate (e.g. 448kbps) AC-3 stream.

[PaulHarald]

Thanks everyone for your excellent replies. Going on holiday now but I'll use Audacity and compare my 256kbps AC3 recordings with my LPCM recordings in some weeks. If what actually gets broadcast is 256kbps sound or "less" then I guess they would look the same, even though It's recorded from a NICAM Stereo broadcast. Should be interesting. I recorded a live show and then some missing tracks of the same show from a rebroadcast, so I have some of the tracks recorded in both formats.

Again: Thanks people. This site is awesome.

[Five]

Paul,

thanks for the props

if you would be so kind we would love to see some screenshots and read your comments about the comparison if you'd like to share that with us.

-J

[PaulHarald]

Of course! But it will be mid-august until I'm back in business :-)

I'm compiling a short live show from the best possible sources, so I'll educate myself along the way. Sources are partially 256kbps AC3, 384kbps AC3 and LPCM. Basically I will use MPEG Streamclip for the Mac to convert the audio streams from the VOB files to AIFF and use Bias Peak to edit the fade in/out and transitions and that's it.

For some reason I have better sounding results using MPEG Streamclip to do it this way, than demuxing first and then go AC3 -> AIFF. Strange. I wonder how this turns out with the PCM audio in this case as I have never tried that. Will do some experimenting and share the freq analysis pics when I get there.

[ssamadhi97]

for the record, you cannot generally compare audio quality by looking at pictures.