关于声学的基本知识

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Understanding dBV, dB, dBFS, dBSPL
[size=13.3333px]So in recap, a "naked" dB has no absolute meaning (though it can be worked out if enough information is known), while a "suffixed" dB always has an absolute meaning because it is in reference to some standard. The reason we have so many suffixes -- dBu, dBm, dBV, dBSPL, dBFS, etc. -- is because we have so many different kinds of things we want to measure. The only catch is to make sure you're referencing apples to apples. [size=13.3333px]

[size=13.3333px]And for all that, it's hopefully clear that the simple reason we use logarithmic scales is because it makes the numbers easier to work with. With practice "thinking logarithmically" will become second-nature and you'll realize that it is indeed worth the effort.

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FFT Size and FFT Range

The larger the FFT size, the greater the frequency resolution of the spectrum, but requiring longer processing times. The FFT size can be set to 128, 256, 512, 1024, 2048, 4096, 8192 or 16384. Since a FFT spectrum contains real and imaginary components, the extracted magnitude spectrum is only half the size. For best response on slower single core devices, keep the FFT size low.

The FFT range can be set to 1.1 kHz, 2.2 k Hz, 5.5 kHz, 11 kHz or 22 kHz. By performing an FFT over a smaller frequency range with the same number of points, much better resolution can be achieved - although also requiring a longer sample of data.