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I am trying to understand the spectrum of the sound of a cuckoo. It is 13-second audio clip and its download link is

https://file.io/d4nqddrb1NNY

Actually, I have a confusion, I have attached a snap of research gate where sound levels are mentioned with + db sign. I have also attached a snap of the spectrum of this audio that I got in Audacity. Why do we have a negative sign here with dB values? Shouldn't it be a positive sign like the values shown on researchgate?

enter image description here

enter image description here

Jdip
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DSP_CS
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    This has to do with scaling. It quite often depends on the Fourier Transform implementation too. Moreover, most probably, what you see there is in dBFS (Full Scale), which is quite widely used in digital systems. The dBFS scale is a logarithmic scale (hence the dB) with its maximum reaching out to 0, with it being the maximum peak attainable value of the digital system. Thus, all values but the maximum have negative values (since the fraction in the logarithm has the maximum value in the denominator and it is always but for the highest value negative). – ZaellixA Aug 08 '23 at 10:05
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    Does this answer your question? – Ahsan Yousaf Aug 08 '23 at 10:26
  • No, it should not be a positive sign, LECS. How do you arrive at the conclusion that it should? – Marcus Müller Aug 08 '23 at 11:42
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    Does this answer your question? What is the audible level for digital audio dB units? – lennon310 Aug 08 '23 at 12:20
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    Regarding your latest update: these are dB(A), meaning they are dB SPL (referenced to 20 micropascals, see Justme’s answer), but “A-weighted” to account for humans perception of loudness. You would benefit from a good read on decibels and the different measures used (dBSPL, dBFS, dBA, dBu etc). Google is your friend for this one. – Jdip Aug 09 '23 at 09:16

1 Answers1

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The audio amplitude of 100% is full scale and that will be 0 dB in comparison to the 100% full scale. That's the amplitude of 1.0 in Audacity.

As your audio amplitude is not full scale 100% but less, the decibel scale is always negative referenced to full scale.

If you are expecting positive decibel values, it likely comes from the fact that sound pressure is referenced to (approximately) the smallest audible level to humans, 20 micropascals, and therefore, all sounds that are louder than this must have positive dB values.

So, these decibels have different reference levels - the digital audio being commonly referenced in dBFS (decibels compared to full scale of 100% amplitude) and sound waves in air in dB SPL (decibels compared to 20 uPa).

Justme
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