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+--- Thread: The formula of deecibel calibration (/showthread.php?tid=1857)
The formula of deecibel calibration - launcher - 01-26-2024
I did some experiments about Audio Amplitude , but I have three question about calibration.
Questions
- What is "Calibration offset"?
- What is the formula of "Calibration offset"?
- What is the formula of Refebrence SPL , and how is it calibrated from the original value?
If you know something about these question , send posts here , please.
RE: The formula of deecibel calibration - Jens Noriʇzsɔɥ - 01-26-2024
The audio signal is not normalised so phyphox cannot relate it to any physics quantities. The SPL (in dB) is log based so any proportionality factor becomes a summand, however, still unknown. If you have a reference signal with a known SPL, you can enter it in the “Calibration” tab and tap “Calibrate“. This automagically computes an offset. Please note that the SPL depends on the distance to the sound source.
There is quite some intricacy to the calibration process. You could find some (further) notes on this in the “FAQ” tab and at our wiki, https://phyphox.org/wiki/index.php/Experiment:_Audio_Amplitude, that is linked from the three-vertical-dots menu.
RE: The formula of deecibel calibration - launcher - 01-29-2024
(01-26-2024, 04:33 PM)Jens Noriʇzsɔɥ Wrote: The audio signal is not normalised so phyphox cannot relate it to any physics quantities. The SPL (in dB) is log based so any proportionality factor becomes a summand, however, still unknown. If you have a reference signal with a known SPL, you can enter it in the “Calibration” tab and tap “Calibrate“. This automagically computes an offset. Please note that the SPL depends on the distance to the sound source.
There is quite some intricacy to the calibration process. You could find some (further) notes on this in the “FAQ” tab and at our wiki, https://phyphox.org/wiki/index.php/Experiment:_Audio_Amplitude, that is linked from the three-vertical-dots menu.
Thank you for answering my question!!
Does that mean that even if I know the SPL correction value for multiple data, I cannot compare those data?
RE: The formula of deecibel calibration - Jens Noriʇzsɔɥ - 01-30-2024
(01-29-2024, 10:41 AM)launcher Wrote: Does that mean that even if I know the SPL correction value for multiple data, I cannot compare those data?
Hm, I am not sure that I understand your question, sorry.
You cannot expect that the offset is identical for different devices. Once calibrated, you should obtain reliable results with this one smartphone – within the limitations of the imperfect audio hardware.
Simple comparisons should always work: louder stays louder regardless of the offset. If your audio signal stays in a rather small frequency band, SPL differences should be even quite ok (no offset needed here).