### F0 Range and F0 Normalization  
When we refer to the 'F0 range' of a particular speaker, there can be diverse meanings. In clinical studies, there is a need to detect the F0 range of a given speaker to diagnose whether the patient has a voice disorder. To this end, [15] defined two types of F0 range: (a) The maximum phonational F0 range (MPFR), indicating the maximum F0 range that a speaker is capable of producing and sustaining with normal phonation (including modal and falsetto registers); (b) The range of speaking F0 (SF0), reflecting a speaker's F0 range adopted in his/her running speech. The SF0 is expected to be at a roughly predictable location in the MPFR of the same speaker. Using whichever type of F0 range, pathologists are able to diagnose vocal fold lesions if the F0 range deviates from its typical setting.  
Among these two types of F0 range, the range of speaking F0 (SF0) is more concerned in linguistic and paralinguistic studies of running speech. [15] did not further clarify the definitions of speaking F0 range, but as a matter of fact there are two ways to define the term. In many cases, the term represents the surface F0 range in the present sample of the speaker's running speech, and thus it can simply be measured by the difference between the minimum and maximum F0 values observed in the speech sample. In other cases, the term refers to the underlying speaking F0 range of a speaker, which is usually not fully displayed in the present speech sample, but instead it is a characteristic of the speaker-specific use of vocal vibration [16; 17].  
In comparison, the surface F0 range is determined simultaneously by the linguistic factors associated with the content of the speech (e.g., in Mandarin, a syllable of the high-falling tone T4 has a wider F0 range than that of the high-flatting tone T1), the paralinguistic factors associated with the emotional/attitudinal state or speaking style of the speaker, and the nonlinguistic factors associated with the speaker-specific physiological traits (e.g., gender, age, and health condition) of the speaker [9; 18; 19; 20; 21; 22; 23; 24; 25] whereas the underlying speaking F0 range is only attributed to the speaker-specific nonlinguistic (mostly physiological) factors, regardless of what content he/she says and in what states/styles he/she says. Apparently, the larger and the more variable the speech sample is (i.e., when there are more linguistic and paralinguistic variations), the better the measured surface F0 range approximate the underlying speaking F0 range.  
In linguistic/paralinguistic studies and speech technologies, there is often a need to estimate the underlying speaking F0 range of a given speaker for the purpose of pitch normalization. Because F0 contours of speech convey not only linguistic but also para/non-linguistic information, a decoding of the phonological pitch targets as well as a decoding of the emotional/attitudinal states needs to rule out the F0 variation attributed to individual difference. This process of normalization is based on an effective estimation of the speaker-specific underlying speaking F0 range. Although human listeners are effortless in pitch normalization, the internal perceptual mechanism is yet to be disclosed, and an efficient algorithm of F0 range estimation is yet to be developed for speech technologies.