One image is using the voltage setting in Spectrum Lab and the other is using th dBFS setting. It illustrates that even the same program with with the same signal can display it in two different ways depending on what you want it to show. Just because the data looks different in each screen shot doesn't mean that one is wrong.
Originally Posted by Shreds
2. -Why haven't you shown us screen caps of the programs they use vs. SL with movie content to prove your points for your argument? Isn't your whole thing about using something other than SL because SL isn't accurate?
Spectrum Lab is accurate which I've explained many times in this thread. As illustrated above, different doesn't have anything to do with accuracy.
Let me ask you a similar question. Why would you use an oscilloscope if Spectrum Lab is accurate? Spectrum Lab is capable of showing the voltage requirements at each frequency. When the 10 Hz tone is playing in Edge of Tomorrow, what is the total output voltage of the signal? You can't tell because you can't tell from the Spectrum Lab graph which other signals are playing at the same time. You need to use an oscilloscope to measure the output voltage for the entire signal. Both tools are accurate, but are showing different info of the same signal.
Telling people their system needs to be capable of reproducing a 10 Hz signal at 937.7 millivolts is meaningless because people don't think of output as voltage. They think of output as SPL. The subwoofer measurements at data-bass are of max burst, basic response, long term output, etc. are showing SPL.
Spectrum Labs is showing maximum power at any given frequency, but is not showing how that energy relates to SPL. If someone wants to know the SPL requirements they need to measure using an RTA like the 1/48 RTA in REW. Nobody is doing that and showing graphs. It just so happens that an FFT, like Spectrum Lab, can have the response tilted by around 3 dB per octave and it will get close to representing the SPL. If people understand this, they can relate the Spectrum Lab peak hold and long term average graphs to actual SPL - when they are comparing to other graphs that use SPL. As far as comparing their own systems to the original signal, then the waterfall graph in SpecLab is best for that. Nobody is arguing that it isn't.
Perhaps the audio analysis software, Spectrafoo, can help clear this up. Spectrafoo is used by many mastering engineers and live sound mixers because it gives so much information about the sound, music, phase, etc. Spectrafoo has an FFT. It is described like this:
SpectraFoo’s underlying FFT generates more data than can be displayed on screen at once. The way that this data is treated when the system computes the trace is called the accumulation mode. SpectraFoo provides two accumulation modes that you can choose using the Spectragraph Controls window:
1. When the Accumulation Mode is set to White Noise is Flat, the Spectragraph shows the maximum power of all of the spectral lines in the FFT that fit into each point in the displayed trace. This has the effect displaying white noise (or noise that has an equal amount of power at each frequency) as a flat line. This mode is traditionally used when the frequency scale of the graph is linear.
2. When the Accumulation Mode is set to Pink Noise is Flat, the Spectragraph shows the sum of the power of all of the spectral lines in the FFT that fit into each point in the displayed trace. This has the effect of displaying pink noise (or noise that has an equal amount of power in each octave) as a flat line. This mode is traditionally used when the frequency scale of the graph is logarithmic and corresponds to the type of display available on a traditional RTA.
The figures below show the results of the two weighting accumulation modes with the two different kinds of noise.
If you understand how an oscilloscope provides you with the sum of all voltages at all frequencies and Spectrum Lab shows you the maximum voltage at each frequency, then perhaps you can begin to understand how Spectrum Lab shows you the maximum power at each point in the FFT while an RTA shows you the sum of power at each point in the FFT. The sum of power is also know as sound power level. The sound power level without distance is the same as the sound pressure level (SPL).