18 Feb
2011
18 Feb
'11
9:16 p.m.
From: Fons Adriaensen <fons(a)linuxaudio.org>
On Fri, Feb 18, 2011 at 07:36:44AM +1300, Jeff McClintock wrote:
Isn't a VU Meter a standard root-mean-square function followed by a 300ms
integration to give it some 'weight'? ...calibrated against a 1kHz tone?
With a RMS VU Meter you measure a 1KHz tone as a
reference.
A contradiction... A VU does not measure RMS, whatever does measure
RMS is not a VU. 
18 Feb
18 Feb
9:44 p.m.
New subject: Calculate R M S (Alfs Kurmis)
On Sat, 19 Feb 2011 09:16:32 +1300
"Jeff McClintock" <jef(a)synthedit.com> wrote:
Maybe that's what some people would like it to be, but all the ones I've seen
have quite different properties from each other. I've yet to see VU meters on
different kit track together :(
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
From: Fons
Adriaensen <fons(a)linuxaudio.org>
On Fri, Feb 18, 2011 at 07:36:44AM +1300, Jeff McClintock wrote:
Isn't a VU Meter a standard root-mean-square function followed by a 300ms
integration to give it some 'weight'? ...calibrated against a 1kHz tone? With a RMS VU Meter you measure a 1KHz tone as a
reference.
A contradiction... A VU does not measure RMS, whatever does measure
RMS is not a VU. 
10:05 p.m.
New subject: Calculate R M S (Alfs Kurmis)
On Sat, Feb 19, 2011 at 09:16:32AM +1300, Jeff McClintock wrote:
No. VU meters were used in the times when audio equipment was using
tubes (valves) so they could not use complex electronic processing,
at most an amplifier stage to drive a bridge rectifier and a passive
moving coil meter. So, ignoring the rectifier threshold, the current
driving the meter would be the absolute value of the signal, not the
square of it. The meter itself is equivalent to a second order lowpass
filter, and its response was quite strictly specified. For a steady
signal, it should rise to 99% of the final value in 300ms, and overshoot
it by 1 to 1.5% before falling back to the real value. The overshoot
isn't a detail - it has quite a marked effect on the response.
Many software 'VU' meters use a first order lowpass - this doesn't
even come close to the response of a the real thing.
Ciao,
--
FA
From: Fons
Adriaensen <fons(a)linuxaudio.org>
On Fri, Feb 18, 2011 at 07:36:44AM +1300, Jeff McClintock wrote:
Isn't a VU Meter a standard root-mean-square function followed by a 300ms
integration to give it some 'weight'? ...calibrated against a 1kHz tone? With a RMS VU Meter you measure a 1KHz tone as a
reference.
A contradiction... A VU does not measure RMS, whatever does measure
RMS is not a VU.
10:19 p.m.
New subject: Calculate R M S (Alfs Kurmis)
On Fri, 18 Feb 2011 21:05:36 +0000
Fons Adriaensen <fons(a)linuxaudio.org> wrote:
<snip>
The overshoot
isn't a detail - it has quite a marked effect on
the response.
Many software 'VU' meters use a first order lowpass - this doesn't
even come close to the response of a the real thing.
Ciao,
Hmmm.
Remembering my early training... In quality moving coil test meters this was
referred to as critical damping and not only gave the best response time but
also gave confidence that the meter needle wasn't sticking. With dead-band
damping where the needle slowed to a stop as it rose (or fell) you were always
tapping the glass because you weren't *quite* sure.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
10:27 p.m.
New subject: Calculate R M S (Alfs Kurmis)
On 18 February 2011 21:19, Folderol <folderol(a)ukfsn.org> wrote:
Remembering my early training... In quality moving
coil test meters this was
referred to as critical damping and not only gave the best response time but
also gave confidence that the meter needle wasn't sticking.
There's a really good user-interface insight in there -- the same one
as exploited in touch-scrolling on certain famous handheld devices,
the sort where scrolling "bounces" when you reach the end...
Chris
10:39 p.m.
New subject: Calculate R M S (Alfs Kurmis)
On Fri, Feb 18, 2011 at 09:27:14PM +0000, Chris Cannam wrote:
On 18 February 2011 21:19, Folderol
<folderol(a)ukfsn.org> wrote:
Yep. Never looked into this, but good filter design is probably
the essence of this sort of thing. The difference between 1st
and 2nd order would be really obvious for something like scrolling.
Ciao,
--
FA
Remembering my early training... In quality
moving coil test meters this was
referred to as critical damping and not only gave the best response time but
also gave confidence that the meter needle wasn't sticking.
There's a really good user-interface insight in there -- the same one
as exploited in touch-scrolling on certain famous handheld devices,
the sort where scrolling "bounces" when you reach the end...
10:28 p.m.
New subject: Calculate R M S (Alfs Kurmis)
On Fri, Feb 18, 2011 at 09:19:27PM +0000, Folderol wrote:
Normally MC meters should be critically damped which means *no* overshoot.
But the VU was explicitly specified as underdamped. That is one of the reasons
why real VUs are not cheap: you can't use a general-purpose MC meter to make a
VU, you need one that was specifically designed for that purpose.
Ciao,
--
FA
isn't a
detail - it has quite a marked effect on the response.
Many software 'VU' meters use a first order lowpass - this doesn't
even come close to the response of a the real thing.
Hmmm.
Remembering my early training... In quality moving coil test meters this was
referred to as critical damping and not only gave the best response time but
also gave confidence that the meter needle wasn't sticking. With dead-band
damping where the needle slowed to a stop as it rose (or fell) you were always
tapping the glass because you weren't *quite* sure. 
19 Feb
19 Feb
10:54 a.m.
New subject: Calculate R M S (Alfs Kurmis)
Le Fri, 18 Feb 2011 21:05:36 +0000,
Fons Adriaensen <fons(a)linuxaudio.org> a écrit :
On Sat, Feb 19, 2011 at 09:16:32AM +1300, Jeff
McClintock wrote:
No. VU meters were used in the times when audio equipment was using
tubes (valves) so they could not use complex electronic processing,
at most an amplifier stage to drive a bridge rectifier and a passive
moving coil meter. So, ignoring the rectifier threshold, the current
driving the meter would be the absolute value of the signal, not the
square of it.
Such indicators shows the average value of the signal, not the
instantaneous value. In case of DC, they are the same, but they are
quite differents in case of AC signals like audio. That is why the
needle should never exceed -6db when recording with old analog
equipment.
The exact value you should not exceed depend of the kind of music you
are recording.
From:
Fons Adriaensen <fons(a)linuxaudio.org>
On Fri, Feb 18, 2011 at 07:36:44AM +1300, Jeff McClintock wrote:
Isn't a VU Meter a standard root-mean-square function followed by a
300ms integration to give it some 'weight'? ...calibrated against a
1kHz tone? With a RMS VU Meter you measure a 1KHz tone as a
reference.
A contradiction... A VU does not measure RMS, whatever does
measure RMS is not a VU. The meter itself is equivalent to a second order
lowpass
filter, and its response was quite strictly specified. For a steady
signal, it should rise to 99% of the final value in 300ms, and
overshoot it by 1 to 1.5% before falling back to the real value. The
overshoot isn't a detail - it has quite a marked effect on the
response. Many software 'VU' meters use a first order lowpass - this
doesn't even come close to the response of a the real thing.
Ciao,
--
"We have the heroes we deserve."
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days inactive
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7 comments
5 participants
participants (5)
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Chris Cannam -
Dominique Michel -
Folderol -
Fons Adriaensen -
Jeff McClintock