Speech coding

speech codecspeech encodingspeechspeech coderspeech compressionvoice compressionspeech codecsvoice codeca categoryanalysis by synthesis
Speech coding is an application of data compression of digital audio signals containing speech.wikipedia
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Vocoder

vocodedvocodersvocoding
4) Vocoders
A vocoder (, a portmanteau of voice and encoder) is a category of voice codec that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption, voice transformation, etc.

Data compression

compressionvideo compressioncompressed
Speech coding is an application of data compression of digital audio signals containing speech.
Compression of human speech is often performed with even more specialized techniques; speech coding, or voice coding, is sometimes distinguished as a separate discipline from audio compression.

Code-excited linear prediction

CELPcode excited linear predictionCode-excited linear prediction (CELP)
The most common speech coding scheme is Code Excited Linear Prediction (CELP) coding, which is used for example in the GSM standard.
Code-excited linear prediction (CELP) is a speech coding algorithm originally proposed by M. R. Schroeder and B. S. Atal in 1985.

Adaptive Multi-Rate Wideband

AMR-WBWBAMR
AMR-WB for WCDMA networks
Adaptive Multi-Rate Wideband (AMR-WB) is a patented wideband speech audio coding standard developed based on Adaptive Multi-Rate encoding, using similar methodology as algebraic code excited linear prediction (ACELP).

Codec 2

Codec2 is another free software speech coder, unencumbered by patent restrictions, which manages to achieve very good compression, as low as 700 bit/s.
Codec 2 is a low-bitrate speech audio codec (speech coding) that is patent free and open source.

G.711

ITU G.711A-lawG.711.1
From this point of view, the A-law and μ-law algorithms (G.711) used in traditional PCM digital telephony can be seen as an earlier precursor of speech encoding, requiring only 8 bits per sample but giving effectively 12 bits of resolution.
G.711 is a waveform speech coder

Speex

SPX.spxlibspeex
G.722, G.722.1, Speex, IP-MR and others for VoIP and videoconferencing
Speex is an audio compression format specifically tuned for the reproduction of human speech and also a free software speech codec that may be used on VoIP applications and podcasts.

Voice over IP

VoIPvoice over Internet Protocolvoice-over-IP
G.722, G.722.1, Speex, IP-MR and others for VoIP and videoconferencing The two most important applications of speech coding are mobile telephony and voice over IP. G.723.1, G.726, G.728, G.729, G.729.1, iLBC and others for VoIP or videoconferencing
Various codecs exist that optimize the media stream based on application requirements and network bandwidth; some implementations rely on narrowband and compressed speech, while others support high-fidelity stereo codecs.

Secure voice

voice encryptionsecure telephonesecure
Much of the later works in speech compression was motivated by military research into digital communications for secure military radios, where very low data rates were required to allow effective operation in a hostile radio environment.
Secure voice's robustness greatly benefits from having the voice data compressed into very low bit-rates by special component called speech coding, voice compression or voice coder (also known as vocoder).

Telephony

digital telephonytelephonedigital
From this point of view, the A-law and μ-law algorithms (G.711) used in traditional PCM digital telephony can be seen as an earlier precursor of speech encoding, requiring only 8 bits per sample but giving effectively 12 bits of resolution.
digital speech coding and compression

Full Rate

GSMGSM 06.10GSM Full Rate
Full Rate, Half Rate, EFR, AMR for GSM networks
Full Rate (FR or GSM-FR or GSM 06.10 or sometimes simply GSM) was the first digital speech coding standard used in the GSM digital mobile phone system.

Selectable Mode Vocoder

SMV
SMV for CDMA networks
Selectable Mode Vocoder (SMV) is variable bitrate speech coding standard used in CDMA2000 networks.

Adaptive Multi-Rate audio codec

AMRAMR-NBAdaptive Multi-Rate
Full Rate, Half Rate, EFR, AMR for GSM networks
The Adaptive Multi-Rate (AMR, AMR-NB or GSM-AMR) audio codec is an audio compression format optimized for speech coding.

Enhanced full rate

EFREnhanced Full-Rate (EFR)ETSI GSM enhanced full rate
Full Rate, Half Rate, EFR, AMR for GSM networks
Enhanced Full Rate or EFR or GSM-EFR or GSM 06.60 is a speech coding standard that was developed in order to improve the quite poor quality of GSM-Full Rate (FR) codec.

Half Rate

GSM-HRHalf-Rate (HR)HR
Full Rate, Half Rate, EFR, AMR for GSM networks
Half Rate (HR or GSM-HR or GSM 06.20) is a speech coding system for GSM, developed in the early 1990s.

G.726

ITU-T G.721
G.723.1, G.726, G.728, G.729, G.729.1, iLBC and others for VoIP or videoconferencing
G.726 is an ITU-T ADPCM speech codec standard covering the transmission of voice at rates of 16, 24, 32, and 40 kbit/s.

Linear prediction

linearlySignal predictioncoefficient
In CELP, the modelling is divided in two stages, a linear predictive stage that models the spectral envelope and code-book based model of the residual of the linear predictive model.
In fact, the autocorrelation method is the most common and it is used, for example, for speech coding in the GSM standard.

G.729

G.723.1, G.726, G.728, G.729, G.729.1, iLBC and others for VoIP or videoconferencing
It is officially described as Coding of speech at 8 kbit/s using code-excited linear prediction speech coding (CS-ACELP).

Digital signal processing

DSPsignal processingdigital signal processing (DSP)
Digital signal processing
Specific examples include speech coding and transmission in digital mobile phones, room correction of sound in hi-fi and sound reinforcement applications, weather forecasting, economic forecasting, seismic data processing, analysis and control of industrial processes, medical imaging such as CAT scans and MRI, MP3 compression, computer graphics, image manipulation, audio crossovers and equalization, and audio effects units.

Speech processing

Speechspeech signal processingmachine processing of speech
Speech processing
Speech coding

Digital audio

digital musicaudiodigital
Speech coding is an application of data compression of digital audio signals containing speech.

Speech

spokenspeakingoral
Speech coding is an application of data compression of digital audio signals containing speech.

Estimation theory

parameter estimationestimationestimated
Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream.

Audio signal processing

audio processingaudio processorsound processing
Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream.