How to differentiate level?

The picture above shows "Equal Loudness Contour". It describe when humans are subject to different volume, one perceive sound (tonal balance) differently. 

Think of it as humans' hearing have different frequency response filtering at different volume.

Optimum listening volume sound be around 75-85 dB SPL combined of all frequencies.

Please also think about sound wave in "Time Domain". The peak to peak spike governed the perceived highest volume, depending on the rest of the sound / speech i.e. depending on waveform.

For example, if it was a instantaneous shout, where the peak to peak is assumed to be 1 and assume it is loud. Then when continuous speech / talking / music playing with equal volume all the way for the long time (long time relative to shout) but only have a peak to peak of around 0.5, it may also be perceived as loud.

The reason is due to the total combine time energy, during a certain PERIOD of time frame. Therefore it is necessary to study sound in "Frequency" domain as well as "Time".

There are more to it in "Equal Loudness Contour", one is advice to take up a few textbooks to find out, how it was created, why it was created and other issues.

1. The Human Ears

2. Disclaimer

3. Questions

4. How is sound created?

5. How do sound travel?

6. How loud is loud?

7. How does the ear work?

8. How does the ear work 2?

9. Hairlike Nerve Died

10. How to localize sound?

11. What do we listen for - to?

12. How do we listen?

13. How to differentiate level?

14. What sound can be heard or not?

15. Regular music frequencies area

16. Questions and Answers

17. Example of sound in Frequency Domain

18. Example of sound in Time Domain

19. One prove of human listening in Time Domain

20. Conclusion

21. A New Thought

22. Side notes

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