ANSI SCTE 24-21:2017 pdf download.BV16 Speech Codec Specification for Voice over IP Applications in Cable Telephony.
This document is identical to SCTE 24-21 2012 except for informative components which may
have been updated such as the title page, NOTICE text, headers and footers. No normative changes have been made to this document.
This document contains the description of the BV 16 speech codec’. BV 16 compresses 8 kHz sampled narrowband speech to a bit rate of 16 kb/s by employing a speech coding algorithm called Two-Stage Noise Feedback Coding (TSNFC), developed by Broadcom.
The rest of this document is organized as follows. Section 2 gives a high-level overview of the TSNFC algorithm. Sections 3 and 4 give detailed description of the BV16 encoder and decoder, respectively. The BV 16 codec specification given in Sections 3 and 4 contain sufficient details to allow those skilled in the art to implement bit-streain compatible and functionally equivalent BV 16 encoders and decoders.
2 OVERVIEW OF THE BV16 SPEECH CODEC
In this section, the general principles of Two-Stage Noise Feedback Coding (TSNFC) are first introduced. Next, an overview of the BVI6 algorithm is given.
2.1 Brief Introduction of Two-Stage Noise Feedback Coding (TSNFC)
In conventional Noise Feedback Coding (NFC), the encoder modifies a prediction residual signal by adding a noise feedback signal to it. A scalar quantizer quantizes this modified prediction residual signal. The difference between the quantizer input and output, or the quantization error signal, is passed through a noise feedback filter. The output signal of this filter is the noise feedback signal added to the prediction residual. The noise feedback filter is used to control the Spectrum of the coding noise in order to minimize the perceived coding noise. This is achieved by exploiting the masking properties of the human auditory system.
Conventional NFC codecs typically use oniy a short-term noise feedback filter to shape the spectral envelope of the coding noise, and a scalar quantizer is used universally. In contrast, Broadcom’s Two-Stage Noise Feedback Coding (TSNFC) system uses a codec structure employing two stages of noise feedback coding in a nested loop: the first NFC stage performs short-term prediction and short-term noise spectral shaping (spectral envelope shaping), and the second nested NFC stage performs long-term prediction and long-term noise spectral shaping (harmonic shaping). Such a nested two-stage NFC structure is shown in Figure 1 below.
In Figure 1 above, the outer layer (including the two short-term predictors and the short-term noise feedback filter) follows the structure of the conventional NFC codec. The TSNFC structure in Figure 1 is obtained by replacing the simple scalar quantizer in the conventional (single-stage) NFC structure by a “predictive quantizer” that employs long-term prediction and long-term noise spectral shaping. This “predictive quantizer” is represented by the inner feedback ioop in Figure 1. including the long-term predictor and long-term noise feedback filter. This inner feedback ioop uses an alternative but equivalent conventional NFC structure, where N,(z) represents the filter.ANSI SCTE 24-21 pdf download.