Why is the given sample rate for TV 48 kHz and HD 96 kHz?
Old 26th April 2010
  #1
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Why is the given sample rate for TV 48 kHz and HD 96 kHz?

Hi Guys,

Just wondering why for TV/Film the sample rate is 48 kHz and for High Definition Film it's 96 kHz. I understand why music is typically 44.1 kHz but with film I'm lost. Anyone care to share some pearls of wisdom?

Jamie
Old 26th April 2010
  #2
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it sounds better
Quote
1
Old 26th April 2010
  #3
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soulviasound's Avatar
 

Quote:
Originally Posted by Big Andy View Post
it sounds better
for bats or for us ?
Old 26th April 2010
  #4
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Quote:
Originally Posted by Big Andy View Post
it sounds better
Can someone with actual knownledge and essentially not trolling please answer?

Quote:
Originally Posted by soulviasound View Post
for bats or for us ?
That's my point, why does it sound better? What makes it better than using 44.1 kHz?
Old 26th April 2010
  #5
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Higher sample rate GREATLY adds to the top end. Listen to an orchestral recording at 96k then listen to a down sampled 44.1k version of the same piece. There is a great loss of depth and clarity on the top end. You can actually hear the room in a 96k recording.

And ps: I'm not trolling, I'm giving you the reason HD Video is at 96k. Nothing Technical about it.
Old 26th April 2010
  #6
All the HD video I post here is 48khz. Just as with DVD, HD video formats may support 96khz, but old habits die hard.
Old 26th April 2010
  #7
although maybe true, I have yet to deliver an HD project for broadcast that wanted 96Khz... all the stuff we get is 5.1 48Khz 16bit on the spec sheets.

cheers
geo


PS: like 96Khz is going to matter after all the mucking with the audio gets from delivery to your TV set in the corner of your room.
Old 26th April 2010
  #8
Quote:
Originally Posted by georgia View Post
although maybe true, I have yet to deliver an HD project for broadcast that wanted 96Khz... all the stuff we get is 5.1 48Khz 16bit on the spec sheets.

cheers
geo


PS: like 96Khz is going to matter after all the mucking with the audio gets from delivery to your TV set in the corner of your room.
+1000000, especially to the latter.

Old 26th April 2010
  #9
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Hmmm, our master tapes go out as 48k/24bit - what the production company does after that I do not know except things rarely sound as pristine as they did when it left me...
Old 26th April 2010
  #10
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you know I never heard an official answer on this...but I always assumed it was because of the film speeds.

A little basic math tells a lot...

48,000Hz / 30fps = 1600 samples / frame

48,000Hz / 24fps = 2000 samples / frame

44,100Hz / 30fps = 1470 samples / frame

44,100Hz / 24fps = 1837.5 samples / frame

This may have nothing to do with it at all. Like I said, I've never heard any official word as to why film and TV uses 48KHz instead of 44.1KHz... but if you look at the timing, when shooting film at 24fps 44.1KHz audio won't sync perfectly.

Also, another factor could be that way, way, way back when DAT tapes first starting being manufactured, they were making them at 48KHz only to help stop piracy (at 48KHz you couldn't just directly dump the DAT onto CD). Maybe that was a factor as well? Small portable digital tape recorders (DAT machines) were all 48KHz originally... and so it stuck with TV and film?

I'd be interested in finding out the true answer myself. All of this is just speculation. Anyone know for sure?
Old 26th April 2010
  #11
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96khz for HD audio? First i've heard of it!

There may be some specialist music projects that do this, but for TV & film...forget it!
Old 26th April 2010
  #12
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48khz was from Dat for Film & TV accuisition of that Im sure.
But the same reason to go highr in sample rate is as true then as it is now, filter design. The simpler the design to filter out the crap above Nyqvist the better the sound below Nyquist will sound.
Old 26th April 2010
  #13
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My understanding is for Tv if it's going to a network, most that are using physical tape like a Digi Beta, the audio can only only max'd out at 48k.
Old 26th April 2010
  #14
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Thanks guys, you've all helped alot. I read somewhere that 96 kHz can be found in HD stuff. This is all for a college assignment, I took Music Technology and we're exploring different sample rates, what they mean and why they actually are how they are. You've all been great help so far any more information would be massively appreciated too

Thanks
Old 26th April 2010
  #15
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Marketing might be one possible reason for having audio at 96KHz
Old 26th April 2010
  #16
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Quote:
Originally Posted by Haydn View Post
Marketing might be one possible reason for having audio at 96KHz
What do you mean? I don't really know much about post production so pardon my ignorance!
Old 26th April 2010
  #17
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Quote:
Originally Posted by Haydn View Post
Marketing might be one possible reason for having audio at 96KHz
If marketing had anything to do with it, it would probably be .mp3, but they would call it ultra-high definition super audio.
Old 26th April 2010
  #18
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44.1KHz is used for CD due to the PCM 1610 (I think) digital back used on U-Matic recorders to make digital masters. it's to do with the frame size and frame rate, that number fitted nicely. 48KHz is used for TV since NICAM (in the UK) has a sampling frequency of 32KHz and before sample rate conversions were easy to do, 48KHz went nicely into 32KHz.

If you were to record everything at 96KHz and work at that throughout the production, you'd be future-proofing your work, and also by the time you came to down convert it would still sound better, since you initially recorded more information. Reverbs and other processing in particular would also sound more natural.

The maximum audible frequency for 96KHz is 48KHz (you have to take at least 2 samples to recreate one cycle of audible frequency - Nyquist) would in theory mean you would need a mic capable of picking up sounds in that frequency range, however, these are very expensive, even with standard mics that go up to 20-25KHz, there would be more clarity in the high end. Analogue systems easily hit 50KHz and above, partly why for very high end stuff they are still preferred (one of MANY reasons).

Hope this helps!
Old 26th April 2010
  #19
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Quote:
Originally Posted by jamiedonnelly View Post
What do you mean? I don't really know much about post production so pardon my ignorance!
I just meant that people who dont understand digital audio could read the number 96k and think that it will sound twice as detailed as 48k.
So high sampling frequencies could potentially be used for marketing even if there were no audible benefits.

Thats quite cynical
Old 26th April 2010
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Quote:
Originally Posted by Haydn View Post
I just meant that people who dont understand digital audio could read the number 96k and think that it will sound twice as detailed as 48k.
So high sampling frequencies could potentially be used for marketing even if there were no audible benefits.

Thats quite cynical

Except there are audible benefits. yes, are ears will not pick up sounds at 48KHz (audible, not sampling frequency), but they will pick up the harmonics from such frequencies that filter down in to our audible range.
Old 26th April 2010
  #21
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kk@jamsync.com's Avatar
 

Quote:
Originally Posted by jamiedonnelly View Post
Hi Guys,

Just wondering why for TV/Film the sample rate is 48 kHz and for High Definition Film it's 96 kHz. I understand why music is typically 44.1 kHz but with film I'm lost. Anyone care to share some pearls of wisdom?

Jamie
48kHz does make for easier math vis a vis frame rate at the bit level for programming video streams. One important reason why you see 48kHz mandated for TV delivery these days is that AC3 (Dolby Digital) has max audio bit rate for audio input defined as 48kHz.

For film, 96kHz is preferable because it can be easily converted to 48kHz, but 96kHz is preferable for Blu-Ray delivery.
Old 26th April 2010
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Quote:
Originally Posted by tom_lowe View Post
Except there are audible benefits. yes, are ears will not pick up sounds at 48KHz (audible, not sampling frequency), but they will pick up the harmonics from such frequencies that filter down in to our audible range.
The damaging effects from the brickwall filter are less at 96kHz because the filter is moved higher in the audio spectrum. I hear the difference in complex metal decaying waveforms of triangles and cymbals, but other than that, it's pretty much a wash. By the time it gets to the typical downstream engineer who squashes the life out of it, 96kHz doesn't matter...
Old 26th April 2010
  #23
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Quote:
Originally Posted by Etch-A-Sketch View Post
you know I never heard an official answer on this...but I always assumed it was because of the film speeds.

A little basic math tells a lot...
48,000Hz / 30fps = 1600 samples / frame
48,000Hz / 24fps = 2000 samples / frame
44,100Hz / 30fps = 1470 samples / frame
44,100Hz / 24fps = 1837.5 samples / frame

This may have nothing to do with it at all. Like I said, I've never heard any official word as to why film and TV uses 48KHz instead of 44.1KHz... but if you look at the timing, when shooting film at 24fps 44.1KHz audio won't sync perfectly.
...
timing is precisely the reason. back in the day, synchronism was actually a big thing. 48000 you can divide by 24, 25, and 30 and get nice whole numbers. not so with 44100. edit: in the case of interlaced TV you'd be looking at dividing by 50 and 60 respectively.

my guess is 96khz is future-proofing the standard in the case of hdtv.

Last edited by gmarinov; 26th April 2010 at 11:06 PM.. Reason: i
Old 26th April 2010
  #24
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Thanks for your help guys, I've learnt alot more than I even needed to and ts a lot more interesting than I thought, I think I'll be lurking the post production forum for pearls of wisdom.
Old 26th April 2010
  #25
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kk@jamsync.com's Avatar
 

Quote:
Originally Posted by gmarinov View Post
timing is precisely the reason. back in the day, synchronism was actually a big thing. 48000 you can divide by 24, 25, and 30 and get nice whole numbers. not so with 44100.

my guess is 96khz is future-proofing the standard in the case of hdtv.
HDTV uses Dolby Digital which is pegged at 48kHz for delivery standards. Unless they develop a much more efficient codec than AC3 it will probably stay there for awhile.
Old 27th April 2010
  #26
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Quote:
Originally Posted by kk@jamsync.com View Post
48kHz does make for easier math vis a vis frame rate at the bit level for programming video streams. One important reason why you see 48kHz mandated for TV delivery these days is that AC3 (Dolby Digital) has max audio bit rate for audio input defined as 48kHz.

For film, 96kHz is preferable because it can be easily converted to 48kHz, but 96kHz is preferable for Blu-Ray delivery.
48KHz was chosed for TV WAAAAAAY before AC-3 was developed. AC-3 maxes out at 48KHz due to the reason I mentioned earlier, not the other way round, the broadcast specs dictated what AC-3 could cope with, the broadcast specs weren't written around AC-3's capability.
Old 27th April 2010
  #27
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Quote:
Originally Posted by gmarinov View Post
timing is precisely the reason. back in the day, synchronism was actually a big thing. 48000 you can divide by 24, 25, and 30 and get nice whole numbers. not so with 44100. edit: in the case of interlaced TV you'd be looking at dividing by 50 and 60 respectively.

my guess is 96khz is future-proofing the standard in the case of hdtv.
The problem with your theory is that NTSC actually runs at 29.97 (my theory is that people the other side of the pond can't actually count properly) which would be 48 000 / 29.97 = 1601.6016 samples per frame, so sorry, but your theory just doesn't add up.
Old 27th April 2010
  #28
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Quote:
Originally Posted by kk@jamsync.com View Post
HDTV uses Dolby Digital which is pegged at 48kHz for delivery standards. Unless they develop a much more efficient codec than AC3 it will probably stay there for awhile.
HDTV doesn't HAVE to use AC-3, they could have gone with AAC, MPEG, Dolby TrueHD, DTS, the list goes on. They stuck with AC-3 for backwards compatibility with home decoders/theatre systems. If they truly wanted 96KHz they could have done so.
Old 27th April 2010
  #29
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But really, the question is:

Why is there air?

Lou
Old 27th April 2010
  #30
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Quote:
Originally Posted by loujudson View Post
But really, the question is:

Why is there air?

Lou
so that sound has something to travel through :-P
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