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| -rw-r--r-- | doc/codec2.pdf | bin | 159985 -> 160852 bytes | |||
| -rw-r--r-- | doc/codec2.tex | 21 |
2 files changed, 13 insertions, 8 deletions
diff --git a/doc/codec2.pdf b/doc/codec2.pdf Binary files differindex 4ca8f32..8d60bb2 100644 --- a/doc/codec2.pdf +++ b/doc/codec2.pdf diff --git a/doc/codec2.tex b/doc/codec2.tex index 22fa749..882f0b3 100644 --- a/doc/codec2.tex +++ b/doc/codec2.tex @@ -62,7 +62,16 @@ pinstyle/.style = {pin edge={to-,thin,black}} \section{Introduction} -Codec 2 is an open source speech codec designed for communications quality speech between 700 and 3200 bit/s. The main application is low bandwidth HF/VHF digital radio. It fills a gap in open source voice codecs beneath 5000 bit/s and is released under the GNU Lesser General Public License (LGPL). It is written in C99 standard C. +Codec 2 is an open source speech codec designed for communications quality speech between 700 and 3200 bit/s. The main application is low bandwidth HF/VHF digital radio. It fills a gap in open source voice codecs beneath 5000 bit/s and is released under the GNU Lesser General Public License (LGPL). + +Key feature includes: +\begin{enumerate} +\item A range of modes supporting different bit rates, currently (Nov 2023): 3200, 2400, 1600, 1400, 1300, 1200, 700C. The number is the bit rate, and the supplementary letter the version (700C replaced the earlier 700, 700A, 700B versions). These are referred to as ``Codec 2 3200", ``Codec 700C"" etc. +\item Modest CPU (a few 10s of MIPs) and memory (a few 10s of kbytes of RAM) requirements such that it can run on stm32 class microcontrollers with hardware FPU. +\item Codec 2 has been designed for digital voice over radio applications, and retains intelligible speech at a few percent bit error rate. +\item An open source reference implementation in the C language for C99/gcc compilers, and a \emph{cmake} build and test framework that runs on Linux/MinGW. Also included is a cross compiled stm32 reference implementation. +\item Ports to non-C99 compilers (e.g. MSVC, some microcontrollers, native builds on Windows) are left to third party developers - we recommend the tests also be ported and pass before considering the port successful. +\end{enumerate} The Codec 2 project was started in 2009 in response to the problem of closed source, patented, proprietary voice codecs in the sub-5 kbit/s range, in particular for use in the Amateur Radio service. @@ -70,6 +79,8 @@ This document describes Codec 2 at two levels. Section \ref{sect:overview} is a This production of this document was kindly supported by an ARDC grant \cite{ardc2023}. As an open source project, many people have contributed to Codec 2 over the years - we deeply appreciate all of your support. + + \section{Codec 2 for the Radio Amateur} \label{sect:overview} @@ -256,14 +267,8 @@ Bit rate & 3200 & 700 \\ Codec 2 is based on sinusoidal \cite{mcaulay1986speech} and Multi-Band Excitation (MBE) \cite{griffin1988multiband} vocoders that were first developed in the late 1980s. Descendants of the MBE vocoders (IMBE, AMBE etc) have enjoyed widespread use in many applications such as VHF/UHF hand held radios and satellite communications. In the 1990s the author studied sinusoidal speech coding \cite{rowe1997techniques}, which provided the skill set and a practical, patent free baseline for starting the Codec 2 project: -Some features of Codec 2: +Some features of the Codec 2 Design: \begin{enumerate} -\item A range of modes supporting different bit rates, currently (Nov 2023): 3200, 2400, 1600, 1400, 1300, 1200, 700 bits/s. These are referred to as ``Codec 2 3200", ``Codec 700C"" etc. -\item Modest CPU (a few 10s of MIPs) and memory (a few 10s of kbytes of RAM) requirements such that it can run on stm32 class microcontrollers with hardware FPU. -\item An open source reference implementation in the C language for C99/gcc compilers, and a \emph{cmake} build and test framework that runs on Linux. Also included is a cross compiled stm32 reference implementation. -\item Ports to non-C99 compilers (e.g. MSVC, some microcontrollers, native builds on Windows) are left to third party developers - we recommend the tests also be ported and pass before considering the port successful. -\item Codec 2 has been designed for digital voice over radio applications, and retains intelligible speech at a few percent bit error rate. -\item A suite of automated tests used to verify the implementation. \item A pitch estimator based on a 2nd order non-linearity developed by the author. \item A single voiced/unvoiced binary voicing model. \item A frequency domain IFFT/overlap-add synthesis model for voiced and unvoiced speech speech. |