is RMS the same as VU level?

[mixaholic]

I have questions. first is RMS the same as VU level and my second question is what VU level should people mix at?

 

[bennychico11]

RMS and VU are two different things...but are usually talked about in conjunction with one another.
VU stands for Volume Unit and is a metering unit in analog equipment that measures signal level. It has a slow response time (usually around 300ms) which ignores peaks and in turn ends up showing the average level during the length of time. This is what usually equates to loudness when heard by the human ear. Contrast this with the peak programme meter found in digital. The VU meter was originally developed for phone lines and was built so that the meters "looked good" with spoken voice. If you want technical jargon:
0 VU is equal to +4 dBm (or 1.228 volts RMS across a 600 ohm load)

RMS stands for root mean square and is a statistical measurement of the overall volume. More jargon:

It is not an average voltage and its mathematical relationship to peak voltage varies depending on the type of waveform. By definition, RMS Value, also called the effective or heating value of AC, is equivalent to a DC voltage that would provide the same amount of heat generation in a resistor as the AC voltage would if applied to that same resistor.

Links:
http://www.eznec.com/Amateur/RMS_Power.pdf
http://en.wikipedia.org/wiki/Root_mean_square
http://www.tpi-thevalueleader.com/rms.html

 

[shackrock]

basically perfect answer. ha.

maybe this will be a little easier for RMS:

say you hooked up a DC source to a load (or speaker, for example), and it put out 100 watts of power.
the RMS value is the AC voltage/current that would provide that same 100 watts to the load/speaker.

 

[SouthSIDE Glen]

0 VU is equal to +4 dBm (or 1.228 volts RMS across a 600 ohm load)

Caution: This is one of those "correct me if I'm wrong" posts...

Not to confuse an already way too confusing subject, but while this is technically true for most gear that outputs a +4 line level, the real-life calibration of VU meters depends to a degree upon the type of unit in which their used, doesn't it?

Typically VU meters are calibrated to a reference level consistant with optimum performance in the device in which they are used. For example, on tape decks, 0VU often corresponds not to the output level of the deck, but rather to a tape mangetization level (measured in nanoWebers) equal to the optimal magnetic field strength for a particular reference tape, the value of which differs depending upon the reference tape standard used.

As such, these particular values for 0VU do not necessarily match the +4dBm output calibration. Am I wrong about that, or is there more equality in VU calibration than I thought?

G.

 

[David Katauskas]

So, if my DAW's master VU meter almost peaks at 0.0 dB, but the RMS is at -15, what does that tell me?

 

[SouthSIDE Glen]

So, if my DAW's master VU meter almost peaks at 0.0 dB, but the RMS is at -15, what does that tell me?

That tells you that you are one of the few people on this board who has thankfully not squashed the s__t out of their dynamics . Or, more technically, that your mix's loudest peaks are at about 0dBFS and ride about 15dB above the "average density" level of your mix.

G.

 

[Massive Master]

So, if my DAW's master VU meter almost peaks at 0.0 dB, but the RMS is at -15, what does that tell me?

Those are NOT VU meters on your DAW.

If your mix is riding around -15dBFS (RMS) then depending on how the converters are calibrated, you'd be somewhere around +3 to +5dBu.

A bit hot for mixing - But it could be worse.

 

[flatfinger]

Go get the free vintage meters at PSP. the default is 0VU reference = -14.0Dbfs

It's nice to set the integer time to 450ms, a little slower than usual.

Lots of good info here:http://www.digido.com/portal/pmodule_id=11/pmdmode=fullscreen/pageadder_page_id=59

 

[Greg_L]

wow. i am so lost.

 

[masteringhouse]

As such, these particular values for 0VU do not necessarily match the +4dBm output calibration. Am I wrong about that, or is there more equality in VU calibration than I thought?

G.

There's the standard, 0 VU is equal to +4 dBm (or 1.228 volts RMS across a 600 Ω load) and then there is the issue of how people actually use the meter. Tape machines can be calibrated at different levels to accomodate various tape formulations in order to take advantage of an increased signal to noise ratio. So yeah, a reading of 0 on a given VU meter doesn't necessarily mean +4 dBm, it depends on how you calibrate your machine.

Here is a nice little calculator showing the standards:

http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/dbconvert/dbconvert.html

Enter 600 for Z0 (ohms), specify sine wave for waveform and 4 for dBm or dBu, it will show 1.228 volts RMS.

There are also standards regarding the ballistics of how a VU should behave. Unfortunately I can't find a link for this standard offhand.

On the digital side of things 0VU typically references -18dBFS, but can be calibrated depending on what type of headroom you want to have available. Lately I've been using -14 dBFS as a standard.