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Dynamics Measured....




I have a pretty crappy scissors here - they don't make a "snip" so instead I popped a Coke can open 4 inches from the microphone.
In one second the levels went from a minimum of 14.7dBA minimum (FAST RMS) to a maximum of 87.5dBA FAST RMS. These FAST time weighted values will correlate (somewhat) to the loudness of the signal. The PEAK pressure on the microphone reached 114.3dB!

That means within less than a 1 second interval an amplifier would have to cover over a 100dB swing in level without clipping. The difference between the MAX level(during the peak) and the Max Peak was 27dB. That 30dB difference requires 1000:1 amplifier headroom! It is a rare recording that shows and preserves that difference.

The Gray "Cursor" and values for that second shown to the right.

The recording engineers place limiters and compressors on the recording or mastering process that prevent that almost 30dB crest factor (Peak to RMS Ratio) of something real! The do this because human hearing doesn't or won't hear the instantaneous peak anyway. And if they recorded the signal preserving the dynamics on the CD, you would be turning your volume knob full clockwise to hear the signal - and then your amplifier would be sure to clip!

The Sound Meter uses TWO 24bit A/D converters overlapped 30dB and sampled at 48kHz to cover the measurement range up to 144dB or so.

Note: the Crappy scissors cutting paper had a Peak level 77.9dB and Max RMS level of 56dB - still a 21dB crest factor - typical recordings are only 13-20dB!

"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius



Edits: 04/20/17

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  Kimber Kable  


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