SONOSAX STELLADAT II - Manual (Page 49)

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5. Applications
Pull up, pull down
A few words of explanation about the Sampling up/down function of the Configuration menu:
The NTSC video standard is used in North America, in several countries of South America, in
Japan and in many other countries. For historical and technical reasons the frame rate of this
system, which was originally 30 frames per second became 29.97 Fr/Sec with the introduction of
color television.
Film runs in the whole world at the speed of 24 Fr/Sec through film cameras. It is projected at
the same speed in theaters. Films are transferred on video for television or for editing on
systems using video pictures. In NTSC countries, the machine used for this transfer, the
telecinema, runs at 23.976 Fr/Sec. That is 0,1% (or 1‰) slower. To remain in sync with the
picture, the sound must also be slowed down by 1‰. This slight slowing down is applied since
long ago on analog sound and works with no other problem than an almost imperceptible slightly
lower pitch.
But in the digital sound world, things are different. One could playback the recordings with a 1 Ω
lower sampling frequency, of course, which has the same effect as slowing down an analog
tape, but most of the digital recorders aren't able to do this. And the AES/EBU standard, which
benefits worldwide recognition, defines that the sampling frequency is 48 KHz (or 44.1 KHz).
Well, if a standard exist, let's respect it!
The solution is quiet simple: All that is necessary is to use, during the recording, a sampling
frequency 1‰ higher (48.048 KHz instead of 48.00 KHz) and so a tape played back for the
telecinema at the AES/EBU standard 48 KHz will run 1‰ slower, at the same speed as the
picture and thus will be in sync with it. Moreover, this solution avoids a sample frequency
conversion, always harmful to the sound quality.
Stelladat II's Sampling up/down option allows exactly to face this problem, in different ways:
Selecting the option Up 1‰, the user has at his disposal a 1‰ higher sampling frequency, thus
48.048 Khz. If the tape is recorded at 44.1 KHz, Up 1 ‰ provides a sampling frequency of
44'144 Hz.
Selecting the Down 1‰ option, Stelladat II can be used to playback tapes recorded at 48 Khz
on other recorders, for a telecinema or a digital video or audio workstation.
What happens with Time Code? If the user selected 30 non drop code at 48.048 KHz, this code
will become 29.97 non drop code if the tape is played back at the standard sampling frequency
of 48 KHz.
Synchronous playbacks for music videos ask the opposite problem and are generally recorded
with a 44.1 KHz sampling frequency with 29.97 (drop or non-drop) Time Code. With Stelladat II,
no special or different recording is necessary: it's enough to playback the music tape on set with
the Up 1‰ option selected, this provides the needed 1‰ fast playback with the 30 necessary
code. No one, other than the playback mixer has to do anything special and he is, after all, the
"specialist" anyway!
(After Manfred N Klemme)