FED-STD 1016
3.9 Error Correction
3 . 9 . 1 Encoding. Forward error correction of 11 bits with a (15,11) Hamming parity code is
provided. The 11 bits protected from a single bit error are:
and
(See section 3.8.2
explanation
of these abbreviations). The 4 parity bits are encoded as follows.
bits
through Hp-3
each represent an even parity computation on 7 of the 11 protected bits as shown below (i.e., a parity
bit is O if the sum of the 7 protected bits is even).
HP-O
)-5,
and SP
)-5,
and Sp
HP- 1
)-6,
and
HP-2
HP-3
and SP
3.9.2 Decoding. The 4 parity bits (HP-0,1 ,2, and 3) shall be used to correct single errors in the 11
protected bits as follows. Parity bits are calculated on the received 11 protected bits as described in
section 3.9.1. Then, these calculated parity bits are Exclusive ORed with the received parity bits.
The following table shows how to correct for a single bit error by reversing the binary value of one
of the protected bits based upon the resulting binary value of the Exclusive ORed parity bits.
Parity Result Invert
Parity Result Invert
3
11
12
5
6
PD( )-7
13
7
14
15
SP
9
10
General Application Notes
3.10
3.10.1 Amplitude Scaling. "Stochastic" elements and gain values contained in this standard are based
upon use of input digitized voice that can assume any integer value in the range -32,768 to
and an impulse of
to calculate the impulse response of the perceptual weighting filter.
3.10.2 Filter Structure. Various filter structures may be used in the implementation of this standard.
All implementations must be interoperable with implementations based upon Direct Form (i.e.,
block-wise) filtering.
3.10.3 Smoothing. It is desirable to employ smoothing to prevent loud clipped voice (i.e., blasts) and
squeaks. Smoothing based upon estimates of the channel error rate (provided by the error correction
mechanism described in section 3.9) is recommended.
4. EFFECTIVE DATE. The use of this standard by U.S. Government departments and agencies is
mandatory effective 180 days after the date of this standard.
5. CHANGES. When a Government department or agency considers that this standard does not
provide for its essential needs, a statement citing specific requirements shall be sent in duplicate to
the General Services Administration (K), Washington, DC 20405, in accordance with the provisions
of Federal Information Resources Management Regulation 41 CFR 201-20. The General Services
Administration will determine the appropriate action to be taken and will notify the agency.