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Old 9th February 2004, 09:54 PM   #1
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Default let peak meter show RMS value !?

Hi,

i am not sure if that is possible analogue but i like to let my analogue peak meter RTW 1206 show true RME value.
is there a schematic available or is this possible to do ??
i knoe that attack time is different to peak..

thanks

Junoman23
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Old 10th February 2004, 06:18 PM   #2
sreten is offline sreten  United Kingdom
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You will have to precondition the signal with a true RMS circiut,
(square the signal value, analogue multiplier, then average it,
the averaging time constant is an issue here.)

Your peak meter will then show the RMS value.

Presumably your meter is the peak hold type, so it will be
showing the peak RMS values of the time constant you have
chosen, unless you have a long time constant, which will just
indicate a relatively steady 10 to 30 dB below peak level.

Perhaps you need VU indication, which is essentially a
RMS indicator with time values suited to analogue tape.

sreten.
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Old 11th February 2004, 06:20 PM   #3
EC8010 is offline EC8010  United Kingdom
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Default Why?

The only reason for using an RMS-reading meter is for measuring power. If the waveform is distorted, yet you need to know the heating effect (power) you truly do need an RMS-reading meter. If you want to measure audio power, then you're only interested in undistorted waveforms, in which case, you just apply the 1 over sqrt 2 scaling factor to your peak reading.

A VU meter is average responding, calibrated RMS of sine wave. Lots of claims are made for VU meters, but the only claim that stands up is that they are cheap.
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Old 11th February 2004, 06:45 PM   #4
sreten is offline sreten  United Kingdom
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Just add the 1 over root 2 scaling will give extremely
misleading results with any peak hold type meter.

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Old 11th February 2004, 08:50 PM   #5
EC8010 is offline EC8010  United Kingdom
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A peak hold meter will give perfectly sensible results using the 1 over root 2 scaling factor provided that an undistorted sine wave is used.

Turning to RMS, power developed by music is irrelevant. What is actually important is the voltage developed across the load. Thus, an amplifier for a tweeter with the same sensitivity as the woofer must develop the same voltage, even though the power dissipated in the tweeter is minimal. The whole point of a peak hold meter is to warn of imminent clipping of devices that don't take kindly to clipping - like AM transmitters and A-Ds, so peak voltage is the correct measure, and RMS would be wrong.
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Old 11th February 2004, 11:10 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
A peak hold meter will give perfectly sensible results using the 1 over root 2 scaling factor provided that an undistorted sine wave is used.

True, but total garbage with music , sreten.
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Old 11th February 2004, 11:50 PM   #7
EC8010 is offline EC8010  United Kingdom
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I have already explained that RMS is not a relevant measure for music (unless you are considering the design of heatsinks or power supplies for class B amplifiers).

Peak is the proper engineering measure for music and any equipment passing it.
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Old 12th February 2004, 12:28 AM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by EC8010
I have already explained that RMS is not a relevant measure for music (unless you are considering the design of heatsinks or power supplies for class B amplifiers).

Peak is the proper engineering measure for music and any equipment passing it.

Basically couldn't agree more.

But as said, peak hold scaled cannot be used to measure
RMS values of music.

Stating that "RMS is not relevant for music" is not remotely
the same as "this method cannot measure music RMS values".

What is missing is what " True RMS " is wanted to
measure, its unlikely this requirement is sensible.

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Old 12th February 2004, 10:16 PM   #9
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hi sreten,

thanksfor the information so far.
my peak meter is a quick responding RTW 1206 which is a quasi standard. is has no peak hold.
http://www.rtw.de/produkte/pr_01/pr01_02.html

i nead to read the relative level or loudness for showing the volume i cut with my vinyl cutting lathe, peak is no so important for that.

where can i get a schematic of a true rms circuit ?

best regards

junoman23
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Old 13th February 2004, 01:41 AM   #10
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I should have thought that a cutting lathe is very definitely an application where peak is important. You have amplifiers driving the cutting head that must not be clipped, a fragile cutting head, and you must ensure that the peak level you cut can be tracked cleanly by a cartridge.

RMS and loudness are not directly related.
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