sipr decode

Decode pitch lag

In the first subframe, a fractional pitch lag is used with resolutions:

• 1/3 in the range [29 1/3; 159]
• 1 in the range [160; 281]

...encoded using 9 bits.

In the second subframe, a pitch lag resolution of 1/3 is always used inthe range [T1 - 10 2/3, T1 + 9 2/3], where T1 is nearest integer to thefractional pitch lag of the previous (1st) subframe. The search rangeis bounded by [30, 281].

Above procedure is applied only if encoded pitch delay is inthe range [0, 61].In the other case the pitch delay is set to T1 + 1, where T1 is nearestinteger to the fractional pitch lag of the previous (1st) subframe.

Decoding of the innovative (algebraic or fixed codebook) vector

Decoding the pulse positions

The fixed codebook vector is reconstructed using 10 pulses in 5 overlapping tracks.Pulses in each track are encoded using 9 bits:

• 1 bit - first pulse's sign (1 - negative, 0 - positive)

• 4 bits - encoded index of first pulse in pair
• 4 bits - encoded index of second pulse in pair