Pitch Estimation and Voiced–Unvoiced Classification of Speech - Digital Speech: Coding for Low Bit Rate Communication Systems - page 172

τ min 1.2 τ i 1.2 τ j 0.8 τ i 0.8 τ j 1.2 τ i 1.2 τ j 0.8 τ j 0.8 τ i τ max

τ i τ j τ i τ j τ j τ i

(a) (b) (c)

Figure 6.20 Three possible pitch-lag search ranges

separately. The smaller range is fully searched and then its minimum error
value is compared with the new candidates in the next bigger range.
The second case (Figure 6.20b) is not as easy as the other two, because
the ranges are only partially overlapping. Assuming the error function is as
sketched in Figure 6.21a, the two search ranges should be fully searched to
prevent the incorrect pitch being selected. However each partly-overlapped
range, R i , can be split into two fully overlapped subranges, R i and R i ,as
shown in Figure 6.21b.

R 4 R 3 R 2 R 1 ∈ ∈ ∈ (6.39)

R 1 R 2 R 3 R 4 ∈ ∈ ∈ (6.40)

E(P)

(a)

τ i τ j

R"4

R'1 R " 3

R'2 R " 2

R " 1

(b)

R'3

R'4

right to left search left to right search

τ 1 τ 2 τ 3 τ 4

Figure 6.21 Partially-overlapped search schematics