RMS - ?

[Umlaaat]

The google search revealed RMS as Root Mean Squared. What I can deduct from this is this is the average level of signal...? But how can this be useful in an audio situation, ie with a compressor or on any other process?

[David@MVS]

Originally Posted by Umlaaat

The google search revealed RMS as Root Mean Squared. What I can deduct from this is this is the average level of signal...? But how can this be useful in an audio situation, ie with a compressor or on any other process?

http://www.rane.com/note134.html

Enjoy,
David

[ShamansDream]

RMS roughly means Perceived Dynamics. You'll never hear the peaks, but you will hear the 'avarage'.

[Zwinter]

RMS, or Root Mean Square, is useful because it tells you the magnitude of the set of numbers. This is important, and it is the reason why you don't use average, because of how negative numbers are treated. Let's say you have a set of numbers: -2, 5, -8, 9, -4. The average of this is zero. The RMS is 6.16, which is arrived at by:
1- square all the values, so in our case you are looking at 4, 25, 64, 81, 16
2- take the average of the squares, which is 38
3- now take the square root, which is the final result of 6.16.

The reason I want to know the magnitude and not an average is because my ears don't hear averages (where you could have all of these huge numbers that cancel out to zero). Our ears, however, do hear magnitude. They hear the differences in sound pressure for both positive (a greater value of pressure) and negative (a lesser value of pressure) values. For example, let’s say that you are in the studio and you see the drivers of your monitors move toward you. That would be increasing the air pressure which will travel to our ears and, hopefully, be heard. The other case is when the driver moves away from you. This is decreasing the air pressure and the end result will be the same; hopefully, you hear it.

So let's take this example even further. Lets say the driver moves toward you and it's magnitude is 5 (which is a arbitrary value for this example), a split second later the woofer moves back to its original position and then another -5 units away from you. The reason I use -5 is to show that it is moving in the opposite direction. The average of these two values is 0. But my ears heard something. So the average is not representing what is really happening. RMS value for this example is 5 which in the case of what my ears heard is a meaningful number.

[Umlaaat]

Originally Posted by Zwinter

RMS, or Root Mean Square, is useful because it tells you the magnitude of the set of numbers. This is important, and it is the reason why you don't use average, because of how negative numbers are treated. Let's say you have a set of numbers: -2, 5, -8, 9, -4. The average of this is zero. The RMS is 6.16, which is arrived at by:
1- square all the values, so in our case you are looking at 4, 25, 64, 81, 16
2- take the average of the squares, which is 38
3- now take the square root, which is the final result of 6.16.

The reason I want to know the magnitude and not an average is because my ears don't hear averages (where you could have all of these huge numbers that cancel out to zero). Our ears, however, do hear magnitude. They hear the differences in sound pressure for both positive (a greater value of pressure) and negative (a lesser value of pressure) values. For example, let’s say that you are in the studio and you see the drivers of your monitors move toward you. That would be increasing the air pressure which will travel to our ears and, hopefully, be heard. The other case is when the driver moves away from you. This is decreasing the air pressure and the end result will be the same; hopefully, you hear it.

So let's take this example even further. Lets say the driver moves toward you and it's magnitude is 5 (which is a arbitrary value for this example), a split second later the woofer moves back to its original position and then another -5 units away from you. The reason I use -5 is to show that it is moving in the opposite direction. The average of these two values is 0. But my ears heard something. So the average is not representing what is really happening. RMS value for this example is 5 which in the case of what my ears heard is a meaningful number.

ok.. innaresting. I understand what you mean.. technically. but how does this work out in real life?

[DeepSpace]

Originally Posted by Umlaaat

ok.. innaresting. I understand what you mean.. technically. but how does this work out in real life?

In real life, RMS is more useful for some things than others.

It is a reasonable approximation of the perceived loudness of a signal.
It is a very good indication of the continuous electrical power required to drive the signal (and of heat dissipation in speakers, transformers etc).
It tells you little or nothing about the size of transient peaks within a signal.

In the days when all equipment was tube equipment, which is a generally more forgiving with regard to transient overload (moderate overs are not so harsh/unmusical), RMS was often the only measure made available and sufficed.

With the advent of solid state and more recently, digital, much of the emphasis has shifted to tracking peaks - and peak metering has become the norm.

Peak and RMS measurements each give you half the story. So the ideal is to have both. Hence, with respect to metering, for instance, some units these days provide both side by side (eg Presonus ADL 600) - a trend that is to be encouraged IMO.