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Topic: Sound level meter / analysis (stereo MP3s) (Read 334 times) previous topic - next topic
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Sound level meter / analysis (stereo MP3s)

In the old days when putting a selection of songs together you could check the volume level with an analogue needle style meter, if it went into the red you could just reduce the volume a little before recording etc.

I have searched for hours online and cannot find anything that does this, everyone goes on about LUFS, RMS, gain etc when I just want to match the volume level.

I tried foobar2000 it analyses a track to just under 10db whereas Audacity says the same track is +0.7db, so one of them is wrong.

To me this is something so fundamental and simply yet I cannot find anything online to support with this. Does anyone know of some basic software that will do this, either graphical or analogue dial format please?

Re: Sound level meter / analysis (stereo MP3s)

Reply #1
Analog vu-meters ( either with needles or with leds) use to show the power of the signal and they are modeled to show values in dBFS ( deciBell respect of Full Scale ).  (Implementations may vary in the way they do it)
Most probably, what you see in audacity is the peak (i.e. the amplitude) of the signal, also in dBFS.

The other mechanisms you mention ( LUFS, RMS... ) are means to know the loudness of a delimited duration of the sound. RMS use to be about 50milliseconds. LUFS can either be an immediate measure (similar to RMS), or a representative measure of the whole duration. 
Their unit is also dB, but it is not dBFS, rather the estimated power produced when played under a predefined setup at a predefined volume. As such, the raw value isn't too useful, but once a reference value is choosen ( 89dB for Replaygain, 85 dB for LUFS, ... ) , the software can say "this tracks is x dB higher than the reference, so the volume has to be reduced by x in order to be played at the reference loudness).

Since you mention recording, analog clipping is quite different than digital clipping. There used to be no problem to go slightly above it. The consequence was some sort of hard limiter, and on playback clipping would depend on the amplifier and the speakers (both distorting the signal)

Since the days of the "Loudness War" (caused by increased amplitude compression), the peak has not been a good measure at all about loudness, and that's the reason why people searched for ways to compare tracks and automatically change its gain, so that the user doesn't need to change the volume from track to track.
In other words: Two tracks with the same peak value could have a difference of 10dB in their perceived loudness.