Internet Low Bit-rate Codec Research Articles

A steganographic method based on gain quantization for iLBC speech streams

Under the premise of ensuring good speech quality and resistance to steganalysis, how to embed as much information as possible into low-bit-rate speech is a challenge. The existing research mainly focuses on least significant bits in the compressed speech streams or line spectral frequencies in the encoding processes of the G.723.1 and G.729a codecs. In this paper, we are concentrating on steganography in Internet Low Bitrate Codec speech streams. Specifically, we present a novel steganographic method on the basis of the gain quantization (GQS), which is included in the vector quantization of dynamic codebooks. The secret information is embedded by modifying the search range of the gain codebook to quantize the gain value. The experimental results show that the proposed GQS method achieves a higher hiding capacity, less signal distortion, and better resistance to steganalysis.

A scalable wideband speech codec using the wavelet packet transform based on the internet low bitrate codec

Most recent speech codecs employ code excited linear prediction (CELP) and transmit side information to improve speech quality under packet loss. Another approach to achieve high robustness to packet loss is to use the frame independent coding scheme based on the internet low bitrate codec (iLBC). The scalable wideband speech codec based on the iLBC was previously presented and outperformed G.729.1 at most bit rates according to the objective quality. This paper presents improvements to the previous work. Specifically, we employ the wavelet packet transform (WPT) instead of the modified discrete cosine transform (MDCT) to enhance the quality, and evaluate the proposed codec based on both the objective and subjective quality measures. The objective quality evaluation results show that clear improvement is achieved and that the proposed codec outperforms G.729.1 at the bit rate of 18 kbps or higher under clean channel conditions and has higher robustness to packet loss than G.729.1. The informal subjective test results also show similar trends.

Steganography in low bit-rate speech streams based on quantization index modulation controlled by keys

Since low bit-rate speech codecs used for voice over internet protocol (VoIP), such as iLBC (internet low bit-rate codec), G.723.1 and G.729A, have less redundancy due to high compression, it is more challenging to embed information in low bit-rate speech streams of VoIP. In this study, a new method is proposed for steganography in low bit-rate speech streams of VoIP. The core idea of this method is setting up a graph model for the codebook space of the quantizer. Based on the graph model, the method realises a quantization index modulation (QIM)-controlled algorithm for partitioning the codebook space. It can be proved that this method can minimize signal distortion while steganography taking place. Taking into account codeword partition balance and partition diversity, the proposed steganographic algorithm was based on QIM controlled by secret keys, i.e., mapping the ways of codebook division into secret keys, thereby significantly improving the undetectability and robustness of VoIP steganography. Performance measurements and steganalysis experiments showed that the proposed QIM-controlled steganographic algorithm was more secure and robust than the QIM algorithm, the conventional RANDOM algorithm and the original codebook algorithm.

An Error Mitigation Technique for Erasure Channels Based on a Wavelet Representation of the Speech Excitation Signal

The importance of packet-based speech transmissions has grown since it offers cheaper and efficient communications. However, frame erasures are a common hurdle in these networks and concealment techniques are necessary to ensure a minimum quality of service. In this paper, we propose a mitigation technique focused on the reconstruction of the linear prediction coding (LPC) coefficients and the excitation signal of the lost frame by using a replacement technique. These replacements are obtained by means of a minimum mean square error estimation based on a source model of the speech parameters (LPC coefficients and the excitation signal). As this approach critically relies on the quantization and representation of the excitation signal, we explore the Haar wavelet transform as a novel approach to represent the excitation signal for error mitigation. Thus, this paper describes how optimal codebook and estimates can be computed in a Haar transformed domain. As a result, the excitation signal of a frame can be decomposed in several partitions where each one is independently reconstructed. Objective and subjective tests are conducted in order to assess the quality of the concealed speech signal resulting from our proposal. Both evaluations confirm noticeable improvements over the default mitigation method included in the two tested standard codecs, adaptive multirate, and Internet low bitrate codec.

Scalable Speech Coding for IP Networks: Beyond iLBC

High quality speech at low bit rates makes code excited linear prediction (CELP) the dominant choice for a narrowband coding technique despite the susceptibility to packet loss. One of the few techniques which received attention after the introduction of CELP coding technique is the internet low bitrate codec (iLBC) because of inherent high robustness to packet loss. Addition of rate flexibility and scalability makes the iLBC an attractive choice for voice communication over IP networks. In this paper, performance improvement schemes of multi-rate iLBC and its scalable structure are proposed, and the proposed codec enhanced from the previous work is re-designed based on the subjective listening quality instead of the objective quality. In particular, perceptual weighting and the modified discrete cosine transform (MDCT) with short overlap in weighted signal domain are employed along with the improved packet loss concealment (PLC) algorithm. The subjective evaluation results show that the speech quality of the proposed codec is equivalent to that of state-of-the-art codec, G.718, under both a clean channel condition and lossy channel conditions. This result is significant considering that development of the proposed codec is still in early stage.

Perceptual evaluation of speech quality for iLBC vocoder with uneven level protection over narrow band MSK radio

Narrow band MSK(Minimum Shift Keying) radio is applied for high receiving sensitive wireless communications like walky-talky. iLBC (internet Low Bit-rate Codec) is widely used in VoIP (Voice over...