What's the purpose of the test tone in a video?

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I transferred a tape from a DVcam to add reverb. What's the purpose of the
test tone at the start of a video? Should it be at any particular level? I
notice the tone on the original tape show to be -8.5 on the left channel
and -8.4 on the right, per the meter on Soundforge. The sound is 2-channel
mono. Also, what about the short "beep" that occurs on "2" of the countdown
in the leader?

I had to lower the level a tad when applying reverb to keep it from
clipping. The highest levels after applying the reverb are about -.7 If I
bring the highest peak back to 0db which is what it appears to be on the
original tape, what considerations should there be regarding the test tone?
Is it imperative to bring it back to the exact same level it was at on the
original tape, which was transferred from a DVCam?

Thanks for all shared wisdom.

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"Doc" wrote ...
>I transferred a tape from a DVcam to add reverb. What's the
> purpose of the test tone at the start of a video? Should it be
> at any particular level?

Frequently, the tone is used as an indication of where the "0dB
reference point" is. The levels of the sound track(s) on the tape
are referenced to this level.

I
> notice the tone on the original tape show to be -8.5 on the left
>channel and -8.4 on the right, per the meter on Soundforge. The
> sound is 2-channel mono.

That is why it is there. So that you can tell where the reference
point is relative to YOUR setup.

> Also, what about the short "beep" that occurs on "2" of the
> countdown in the leader?

It is a (optional) tradition with the "Academy Leader".
It serves several purposes, not the least of which is
to wake up the operator when it is time to switch. :-)

> I had to lower the level a tad when applying reverb to keep
> it from clipping. The highest levels after applying the reverb
> are about -.7 If I bring the highest peak back to 0db which is
> what it appears to be on the original tape, what considerations
> should there be regarding the test tone?
> Is it imperative to bring it back to the exact same level it was
> at on the original tape, which was transferred from a DVCam?

Your new peaks should have the same ratio to your reference
tone as the original peaks had to the original reference tone.
OTOH, I don't think I would be all that obsessive about 0.7dB.
They'll likely not even notice.

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On Wed, 15 Jun 2005 21:46:23 -0700, "Richard Crowley"
<rcrowley7@xprt.net> wrote:

>Frequently, the tone is used as an indication of where the "0dB
>reference point" is. The levels of the sound track(s) on the tape
>are referenced to this level.

-8.5dB. That's an odd value, ain't it.

-martin-

--
"Now I want you to say it thrice daily and don't dress a bun"

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On 16 Jun 2005 08:52:59 -0400, kludge@panix.com (Scott Dorsey) wrote:

>Tone at -20. Always.

YMMV Other countries use -12

-martin-

--
"Now I want you to say it thrice daily and don't dress a bun"

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In article <pvt2b1prn9jquvu638lb9m53t494i5e763@4ax.com>,
Martin Heffels <safeshop77@yahoo.com> wrote:
>On 16 Jun 2005 08:52:59 -0400, kludge@panix.com (Scott Dorsey) wrote:
>
>>Tone at -20. Always.
>
>YMMV Other countries use -12

Again, it doesn't really matter as long as yoou don't clip and you have
the same levels going in as you have coming out.

But it's worth putting a sticker on the tape if it's at -12. Or even
if it's at -20.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On 16 Jun 2005 10:07:29 -0400, kludge@panix.com (Scott Dorsey) wrote:

>In article <pvt2b1prn9jquvu638lb9m53t494i5e763@4ax.com>,
>Martin Heffels <safeshop77@yahoo.com> wrote:
>>On 16 Jun 2005 08:52:59 -0400, kludge@panix.com (Scott Dorsey) wrote:
>>
>>>Tone at -20. Always.
>>
>>YMMV Other countries use -12
>
>Again, it doesn't really matter as long as yoou don't clip and you have
>the same levels going in as you have coming out.

Tell that to the posthouse guys who adjust your -20 to -12 when they
dub it ;-)

>But it's worth putting a sticker on the tape if it's at -12. Or even
>if it's at -20.

That sticker is a must!

cheers

-martin-

--
"Now I want you to say it thrice daily and don't dress a bun"

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Whoa there Scott . . .

My analog roots may be failing me here. Or I may just not be understanding
you.

My operator's understanding - - as opposed to an audio engineer's
understanding - - is that db is a measure of the relative difference between
two audio sources. With that in mind (and correct this underlying
assumption here if it's wrong) . . . .

Are you saying to record the tone 20 db below program audio peaks ? Or
at -20 relative to some external reference. Or some arbitrary voltage
level, etc. ?

In practice - - I'm a operator, remember - - when I make a tape (beta SP)
for a TV station (at least a weekly occurrence at our shop here), I always
reference the tone to 0, and then make sure the peak audio levels make only
brief excursions into the red, never exceeding +4 or so. The audio is
compressed as it's recorded, and handled well along the production chain, so
this isn't too difficult at this stage.

Am I doing something wrong ? I don't think so.

Inquiring minds want to know . . .

Steve




"Scott Dorsey" <kludge@panix.com> wrote in message
news8rsnb$m4p$1@panix2.panix.com...
> Doc <docsavage20@xhotmail.com> wrote:
> >I transferred a tape from a DVcam to add reverb. What's the purpose of
the
> >test tone at the start of a video? Should it be at any particular level?
I
> >notice the tone on the original tape show to be -8.5 on the left channel
> >and -8.4 on the right, per the meter on Soundforge. The sound is
2-channel
> >mono. Also, what about the short "beep" that occurs on "2" of the
countdown
> >in the leader?
>
> The tone should be at - 20dBFS for standard reference. It really only
> matters that nothing clips and that you dub the thing back to DV at
> the same level, though.
>
> The 2-beep is to synchronize sound and picture.
>
> >I had to lower the level a tad when applying reverb to keep it from
> >clipping. The highest levels after applying the reverb are about -.7 If I
> >bring the highest peak back to 0db which is what it appears to be on the
> >original tape, what considerations should there be regarding the test
tone?
>
> Tone at -20. Always.
>
> >Is it imperative to bring it back to the exact same level it was at on
the
> >original tape, which was transferred from a DVCam?
>
> Probably. It would certainly be a good idea. That's why post houses
> have everything set up at the same level and why there is tone on tape.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

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Steve Guidry <steveguidrynospam@earthlink.net> wrote:
>Whoa there Scott . . .
>
>My analog roots may be failing me here. Or I may just not be understanding
>you.
>
>My operator's understanding - - as opposed to an audio engineer's
>understanding - - is that db is a measure of the relative difference between
>two audio sources. With that in mind (and correct this underlying
>assumption here if it's wrong) . . . .

Right.

>Are you saying to record the tone 20 db below program audio peaks ? Or
>at -20 relative to some external reference. Or some arbitrary voltage
>level, etc. ?

In the digital world, the tone is recorded so that it is 20 dB below the
full scale level at which the digital system clips.

>In practice - - I'm a operator, remember - - when I make a tape (beta SP)
>for a TV station (at least a weekly occurrence at our shop here), I always
>reference the tone to 0, and then make sure the peak audio levels make only
>brief excursions into the red, never exceeding +4 or so. The audio is
>compressed as it's recorded, and handled well along the production chain, so
>this isn't too difficult at this stage.

Right. You're using an average-reading meter, and you're seeing levels
4 dB above the tone mark. This means you're seeing peak levels that are
a good bit higher than that, maybe as much as another 6 dB.

Remember, there is no plus-anything on the digital meter. It gets up to
zero, and then it clips. So the digital reference needs to be high enough
so that the tone is -10dBFS with your tape or it'll clip. Setting it at
-20 dBFS gives you another 10dB of safety margin.

>Am I doing something wrong ? I don't think so.

Not at all! You're doing things perfectly. The problem comes in that
your meters are reading in a different way than the digital meters, so
if you dub your tape to a digital recorder, the metering has to be set
differently on the digital recorder.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Steve Guidry <steveguidrynospam@earthlink.net> wrote:
>Oh. That just reflects the 16 db or so headroom that analog gear usually
>has. Plus an extra margin.

You can think of it that way. Some of the "headroom" though, comes from
the difference between peak and average metering and some of it comes from
the fact that the 0dB mark on the meters is not a hard limit with analogue
recorders.

>In practice, on our 'truck shoots" when we record the camera ISO's to DV, we
>usually set our decks 10db down. I'm assuming that we are able to get away
>with it because of our extreme attention to the program audio levels and
>compression before it even gets to the decks. It would be very rare that
>we'd ever have a 10db spike.

That's fine, as long as you have the tapes marked that way so when you
send them to another facility their levels are correct.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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"Scott Dorsey" <kludge@panix.com> wrote in message
news8sccq$t8c$1@panix2.panix.com...

> Not at all! You're doing things perfectly. The problem comes in that
> your meters are reading in a different way than the digital meters, so
> if you dub your tape to a digital recorder, the metering has to be set
> differently on the digital recorder.

Let me bounce this off you. So far I've left the test and timing (?) tones
alone (they're at -8.5) and processed only the performance itself. The
hottest signals on the original file are right at 0db. Well, actually there
are a couple of spots where it actually clips, but for the most part they're
right at 0db according to what the Soundforge meter says. I had to lower the
overall level a bit to allow for the acoustic mirror processing. Then again
using the volume utility, I brought the whole thing (except for the tones)
up to where it peaks at exactly 0db. I used the volume utility instead of
compression (Wave Hammer) to avoid altering the overall character of the
file beyond the reverb.

So, now the test tone is exactly where it was as they gave it to me, and the
highest peaks, though in slightly different places, are back at 0db. The
responses in here indicate that -8.5 is an oddball level for the test tone,
but that's where they had it.

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Doc wrote:
>So far I've left the test and timing (?) tones
> alone (they're at -8.5) and processed only the performance itself. The
> hottest signals on the original file are right at 0db. Well, actually there
> are a couple of spots where it actually clips, but for the most part they're
> right at 0db according to what the Soundforge meter says.

A lot of consumer DV Cams have a built in limiter so you don't get
"overs". When you work with a Tape on a true mixing desk (as opposed
to a DAW), you adjust the trims on your audio channel inputs so that
the tone coming off the tape reads 0VU on your mixing desk. Thing is
that DAW's are a somewhat different paradigm than working on a classic
mixer, and people learning audio on them kind of miss a stage of
learning that you get from working on a real console. A lot of DAW's
don't have the "solo in place" or "prefade listen" functions that a
real console has either.

>I had to lower the
> overall level a bit to allow for the acoustic mirror processing. Then again
> using the volume utility, I brought the whole thing (except for the tones)
> up to where it peaks at exactly 0db. I used the volume utility instead of
> compression (Wave Hammer) to avoid altering the overall character of the
> file beyond the reverb.
>
> So, now the test tone is exactly where it was as they gave it to me, and the
> highest peaks, though in slightly different places, are back at 0db. The
> responses in here indicate that -8.5 is an oddball level for the test tone,
> but that's where they had it.

I might label the tape "0VU = -8.5dbFS" to give a heads up to the
next guy who has to deal with the tape not to take anything for granted
when he does a transfer. 8.5db is about the "crest factor" that
cassette tapes require, that is peak levels not exceeding the VU
(average) levels by more than that. Also if you feed a -10 level
device (like a consumer DV Cam's rca jacks) a +4 line level signal,
what is 0VU @ -20dbFS at a +4 level now hits your -10 device around
-6dbFS. So I might suspect something like that kind of "cheating
levels" was happening for one reason or another when they tracked the
audio on your DV Tape.

Will Miho
NY Music and TV Audio Guy
Staff Audio / Fox News / M-AES
"The large print giveth and the small print taketh away... " Tom Waits
"

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On Jun 16, 2005, Martin Heffels <safeshop77@yahoo.com> commented:

> YMMV Other countries use -12
>--------------------------------snip----------------------------------<

Not the UK, and not the USA. Standard levels for all digital VTRs I know of
(D5, HDCam, D1, D2, etc.) have been -20 for tones for over a decade. Sony
and Panasonic also put that in the manual. The BBC typically requests -18,
but they're the only exception to my knowledge.

Tell me the country that uses -12 and the name of the broadcast venue that
asks for that level.

I have seen -14 used for audio mastering tones, for creating CD master tapes,
but not for video.

--MFW

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On Thu, 16 Jun 2005 23:54:29 GMT, Marc Wielage <mfw@musictrax.com>
wrote:

>Tell me the country that uses -12 and the name of the broadcast venue that
>asks for that level.

Australia, all of it.

-martin-

--
"Now I want you to say it thrice daily and don't dress a bun"

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On Sat, 18 Jun 2005 20:43:38 +1000, "John T"
<hotflashesnil@hotmail.com> wrote:

>Not true, -14 down here.

Where here? At the post-houses we used frequently, The Lab, Video 8,
and the one whose name I always forget in Sydney, it was -12. And they
told me it was -12 all over the country. Maybe I should go back and
kick some arse ;-)

cheers

-martin-

--
"Now I want you to say it thrice daily and don't dress a bun"

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"nobody special" <msu1049321@aol.com> wrote in message
news:1118984242.390844.277370@o13g2000cwo.googlegroups.com...

> Doc, please understand I am not trying to insult you, but frankly, I
> don't see how you can offer yourself as an audio sweetening business if
> you are only now just learning really elemental basics like setting
> tone. This is like a roofing contractor bidding to re-do my house and
> asking me what the heavy silvery thing next tot he nails is for. I
> think maybe you're being ambitious, and rather than see you get in over
> your head, I think you should re-think the "business proposition" with
> the TV station and just work on these at a non-cash "hobby" level while
> you build up more experience.

I didn't actually offer myself as an audio sweetening business. I happened
to mention to a musician friend during the course of conversation that I was
transferring my family movies and video tape to DVD.

When she heard this her ears perked up and she asked if I could convert a
VHS tape of her performance to DVD. I knew this would be a simple enough
task. When I got it, it occurred to me to ask her if she wanted me to add
reverb to it since the sound was dry. She didn't realize you could do that.
She was so tickled with the results that she asked if I could do the same
with the master tape at the studio. I captured that first project with my
DC-10 capture card. In the interim I had acquired a Digital8 camcorder. All
research including a number of inquiries on Usenet indicated that it should
be no problem to capture the DV cam footage It just happened to be good
timing that I had only a few days earlier acquired a cam that could do it.

So, I did it.

Great thing about people, they have the capacity to learn. That's why I'm
asking questions. Despite the fact that I had never touched a digital
camcorder until a couple of weeks ago, and had never actually used the
Firewire port before, and admittedly only have a peripheral understanding of
the various issues involved, it's just as captured and treated using my eBay
consumer digital cam as it would have been by some $200/hr production house.
Keep in mind, it's a pretty basic project. I didn't have to learn to use an
editing suite, just add reverb and take out a few mic thunks in the sound
track using software I was already familiar with.

The station manager was completely aware of all of this, I wasn't trying to
pull the wool over his eyes. I was just doing a project for a friend. He
actually never even mentioned the test tone issue. It's something I thought
to ask about on my own. Since then, he's asked me if I want to work on some
other music programs they have. He hasn't even seen the results of my first
project yet. What can I say. An opportunity has presented itself.