Hi I've recorded sound(field sound) using six microphones with sensitivity 5mv/pa by zoom recording device the results were obtained by dBFS unit and i need it in dBSPL, Is there any way to convert it? because I have read several articles and come to the do not directly convert between the two units and need to calibrate the device and determining the gain, but I recorded directly without doing anything . Another question whether the output values of positive values and negative do it represent the pressure deviation? I'm sorry but I do not have sufficient knowledge with the sound recording instruments. thanks

  • \$\begingroup\$ Quite a disconcerting read. You want to convert between to "units" when you in fact have two different physical quantities on hand. Ask yourself what dB SPL is (what physical quantity it is) and how your recording relates to that. \$\endgroup\$ – winny Dec 30 '16 at 21:25

You could try to go back and retroactively "calibrate" your original recordings. But that requires these things.

  1. FIXED RECORDING LEVELS Your original recording must have been done at some FIXED and unchanging recording level/gain from beginning to end. If you changed the recording levels at one or more points during the recording, then you have no way that any of the next steps will make any sense. Note this includes using any kind of "automatic gain" as that completely destroys your data.
  2. REFERENCE SOUND You need some sound that was captured in the original recording which you can RELIABLY REPRODUCE. That gives you the "link" between your original recording and something that you can actually MEASURE.
  3. SPL METER You need an actual, calibrated SPL meter. There is no substitute for this if you want believable SPL data.
  4. CALIBRATED REFERENCE MEASUREMENT Reproduce your "reference sound" and measure the SPL with the calibrated SPL meter. Then you can use that peak level to measure against your recording levels.
  • \$\begingroup\$ Sorry but I did not understand some of the paragraphs clearly do you mean record a fixed sound level like a sine wave and then re-run the recorded section and measure the SPL by calibrated SPL meter??? \$\endgroup\$ – user130733 Jan 6 '17 at 17:10

Unless you calibrated the microphones AND the recorder at the time of the recording the absolute dB SPL reference is lost and unrecoverable. The reason is that you don't know what what the REAL sensitivity of the microphones are. "5mv/pa" is only the nominal design target. It does not necessarily represent the ACTUAL sensitivity. And only calibrated instrumentation microphones have a known and reliable SPL to voltage output ratio.

Furthermore, you used some unknown amount of gain in the recorder. So even if you had calibrated microphones, you would have no reliable reference unless you calibrated the microphone preamp gains and the recording levels.

  • \$\begingroup\$ Thank you for your answer, but now what should i do? any suggestion to help me to solve the problem @Richard Crowley \$\endgroup\$ – user130733 Dec 27 '16 at 11:19
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    \$\begingroup\$ We don't know what exactly the problem is? WHY do you need dB SPL? Can you explain the situation more completely? \$\endgroup\$ – Richard Crowley Dec 27 '16 at 16:30
  • \$\begingroup\$ I need to calculate the noise for the graduation project and in all the equations we need sound pressure level (dBSPL), but at first I did not know the difference between the two units and I need more than one microphone so used six microphones with Zoom recording device and the result in dB full scale. \$\endgroup\$ – user130733 Dec 27 '16 at 17:34
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    \$\begingroup\$ If you were not using a Sound Pressure Level Meter, there really is no way to go back and "calibrate" your recordings. The major unknown is the recording volume control setting. Unless you know that, there is no realistic way to correlate the recorded level with the actual SPL. Can you repeat the experiment with a proper SPL Meter? \$\endgroup\$ – Richard Crowley Dec 27 '16 at 18:58
  • \$\begingroup\$ If repeated the experiment How can I do calibration \$\endgroup\$ – user130733 Dec 30 '16 at 19:26

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