Author Topic: dB reference war ???  (Read 2021 times)

stereokillah

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dB reference war ???
« on: July 13, 2010, 09:31:24 PM »
hi,
i'm searching some indication about each dB format: dbu, dbvu, dbfs, rms etc...

some time i check my sound with this plugin
this what i found

0 dbu = 0dbvu = 0.7746 volts (RMS)

dbfs is for numrique decibel full scale, but it's not the same  with each converter ADDA

so the RMS on the plugin in the picture is the same as 0dbu ???

 :'( :'( :'( :'(
 i think the answer is no but if it no what is this rms on the plugin room master service?



at time all my material in moving on, i can't make mesure myself

thank you
« Last Edit: July 13, 2010, 10:22:54 PM by stereokillah »
if your neighbour is hunger .. don't give him fish, teach him how fishing ...


MikeFFG

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Re: dB reference war ???
« Reply #1 on: July 14, 2010, 03:04:49 AM »
You got the first part sorta right. 0 dbu = 0 dbv (not dbvu) = .775 v

VU is a type of average metering as opposed to peak metering which reads instantaneous peaks, but VU is not a reference level.

But dbFS has a maximum of zero and should be the same on all converters.  Otherwise there wouldn't be a proper reference between systems.  Some people's 0 would be louder than others and that wouldn't make any sense. 

RMS is root mean square which is basically like VU though a bit different.  This gives you an average level and will always be several db lower than your peak level.

[silent:arts]

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Re: dB reference war ???
« Reply #2 on: July 14, 2010, 09:01:32 AM »
You got the first part sorta right. 0 dbu = 0 dbv (not dbvu) = .775 v
sorry, all wrong.
0 dBu = 0.7746V
0 dBV = 1V = 2,22 dBu
0 VU = (international) +4 dBu = 1,228V
0 VU = (german broadcast) +6 dBu = 1,55V

Quote
VU is a type of average metering as opposed to peak metering which reads instantaneous peaks
correct. but with a 1kHz sine wave only it shoud read the same

Quote
but VU is not a reference level
VU = Volume Unit

Quote
But dbFS has a maximum of zero and should be the same on all converters. Otherwise there wouldn't be a proper reference between systems.  Some people's 0 would be louder than others and that wouldn't make any sense.
it isn't the same on all converters, this is why I never understand people measuring analog gear with their software in dBfs. it says nothing.
there are different standards:
0 dBfs = +14 dBu (Standard used by CBS for the Sony pcm1630 for CD mastering) [thanks Walrus]
0 dBfs = +15 dBu (stupid german broadcast norm. Digidesign even builds a special 192 I/O DA card to reach this norm in germany)
0 dBfs = +18 dBu (IIRC international TV standard)
0 dBfs = +20 dBu (IIRC international cinema standard)
0 dBfs = +24 dBu (some AD/DA converters can manage this, my private home standard :D)

Quote
RMS is root mean square which is basically like VU though a bit different.  This gives you an average level and will always be several db lower than your peak level.
correct
« Last Edit: July 14, 2010, 09:26:23 AM by [silent:arts] »
SSLtech: No bypass, I don't believe in it.
Gus: I think this build might have problems with DIY builders that don't know things like ohms law.

Walrus

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Re: dB reference war ???
« Reply #3 on: July 14, 2010, 09:21:13 AM »
You forgot  0 dBfs = +14 dBu (Standard used by CBS for the Sony pcm1630 for CD mastering)    ;D
Kevin.

[silent:arts]

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Re: dB reference war ???
« Reply #4 on: July 14, 2010, 09:27:36 AM »
added to the list.
if you are in the need of a PCM1630 let me know ;D
but the transformers and JH990s are already stolen ... ;D ;D ;D
SSLtech: No bypass, I don't believe in it.
Gus: I think this build might have problems with DIY builders that don't know things like ohms law.

stereokillah

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Re: dB reference war ???
« Reply #5 on: July 14, 2010, 09:41:37 AM »
thanks for your replys,

therefore rms is not equivalent to dbu or voltage.
right?
if your neighbour is hunger .. don't give him fish, teach him how fishing ...

[silent:arts]

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Re: dB reference war ???
« Reply #6 on: July 14, 2010, 09:45:36 AM »
right
SSLtech: No bypass, I don't believe in it.
Gus: I think this build might have problems with DIY builders that don't know things like ohms law.

JohnRoberts

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Re: dB reference war ???
« Reply #7 on: July 14, 2010, 09:56:44 AM »
Some good info... the classic (archaic) 0 VU= +4 dBm is a power level reference, and agrees with the voltages already given for dBu when terminated by 600 ohms.  

The reason 0 dBfs does not line up to a single analog voltage is because 0dBfs is similar to clipping or max output on analog gear which is also quite variable depending on power supplies used and how the individual designer calibrates his audio path to the outside world..

One could argue that the 0dBfs mindset is setting levels while thinking how much below digital clipping are we. The old school, 0VU was more like targeting some nominal level (actually ballpark 20dB below clipping) to deliver a decent tradeoff between headroom and s/n. The old school (analog) audio paths were perhaps more tolerant of some modest clipping because of the more benign nature of analog clipping especially compared to early digital paths. Since the early digital paths combined nasty clipping with poor dynamic range, one was motivated to hit it as hard as possible without clipping.  

 JR
John Roberts
http://circularscience.com
Tune it, or don't play it...

stereokillah

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Re: dB reference war ???
« Reply #8 on: July 14, 2010, 02:27:25 PM »

ok thank you , I begin to understand a little better

is there a plugin that would give the analise dbu please?
if your neighbour is hunger .. don't give him fish, teach him how fishing ...

[silent:arts]

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Re: dB reference war ???
« Reply #9 on: July 14, 2010, 02:39:29 PM »
knowing your 0 dBfs versus dBu helps.
this is the advantage of dBs ...
just convert some numbers ;)
SSLtech: No bypass, I don't believe in it.
Gus: I think this build might have problems with DIY builders that don't know things like ohms law.


Gold

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Re: dB reference war ???
« Reply #10 on: July 14, 2010, 03:10:41 PM »
0 dBfs = +18 dBu (IIRC international TV standard)
0 dBfs = +20 dBu (IIRC international cinema standard)

I don't think this is totally correct. IIRC EBU and NHK Japan use +18dBu for broadcast and SMPTE in the USA uses +20dbu.

pucho812

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Re: dB reference war ???
« Reply #11 on: July 14, 2010, 11:24:33 PM »
and don't forget that a pro tools 192 interface out of the box is calibrated so that 0VU = -18DBfs, the old tascams da88's were pre calibrated so that 0VU = -16DBfs. The old Yamaha 02r was set so that 0VU = -21DBfs. and so on and so on.
« Last Edit: July 21, 2010, 12:57:49 AM by pucho812 »
Every mic has a purpose it might be a door stop or a hammer, but every mic has a purpose.

robovox

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Re: dB reference war ???
« Reply #12 on: July 20, 2010, 12:59:18 AM »
+4dBu into the Alesis HD24XR measures as -15dBFS, on both the meters and the recorded waveform amplitude. 0dBFS = +19dBu, and that's all, folks.

It took reading Bob Katz's Mastering Audio: the Art and the Science to finally convince me to let go of trying to "use all the bits."
I have an electric grandpa bed that talks to me while I sleep.
                                                              --Dean Venture

pucho812

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Re: dB reference war ???
« Reply #13 on: July 21, 2010, 12:58:15 AM »
+4dBu into the Alesis HD24XR measures as -15dBFS, on both the meters and the recorded waveform amplitude. 0dBFS = +19dBu, and that's all, folks.

It took reading Bob Katz's Mastering Audio: the Art and the Science to finally convince me to let go of trying to "use all the bits."


no need in a 24 bit pcm world...
Every mic has a purpose it might be a door stop or a hammer, but every mic has a purpose.


 

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