diff options
Diffstat (limited to 'gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h')
| -rw-r--r-- | gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h | 97 |
1 files changed, 87 insertions, 10 deletions
diff --git a/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h b/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h index 57734ca15..066a477f4 100644 --- a/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h +++ b/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h @@ -28,6 +28,22 @@ class cvsd_encode_sb; typedef boost::shared_ptr<cvsd_encode_sb> cvsd_encode_sb_sptr; + /*! + * \brief Constructor parameters to initialize the CVSD encoder. The default + * values are modeled after the Bluetooth standard and should not be changed + * except by an advanced user + * + * \param min_step Minimum step size used to update the internal reference. Default: "10" + * \param max_step Maximum step size used to update the internal reference. Default: "1280" + * \param step_decay Decay factor applied to step size when there is not a run of J output 1s or 0s. Default: "0.9990234375" (i.e. 1-1/1024) + * \param accum_decay Decay factor applied to the internal reference during every interation of the codec. Default: "0.96875" (i.e. 1-1/32) + * \param K; Size of shift register; the number of output bits remembered by codec (must be less or equal to 32). Default: "32" + * \param J; Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4" + * \param pos_accum_max Maximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT) + * \param neg_accum_max Minimum integer value allowed for the internal reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1) + * + */ + cvsd_encode_sb_sptr cvsd_make_encode_sb (short min_step=10, short max_step=1280, double step_decay=0.9990234375, @@ -37,6 +53,60 @@ cvsd_encode_sb_sptr cvsd_make_encode_sb (short min_step=10, short pos_accum_max=32767, short neg_accum_max=-32767); +/*! + * \brief This block performs CVSD audio encoding. Its design and implementation + * is modeled after the CVSD encoder/decoder specifications defined in the + * Bluetooth standard. + * + * \ingroup block + * + * CVSD is a method for encoding speech that seeks to reduce the + * bandwidth required for digital voice transmission. CVSD takes + * advantage of strong correlation between samples, quantizing the + * difference in amplitude between two consecutive samples. This + * difference requires fewer quantization levels as compared to other + * methods that quantize the actual amplitude level, reducing the + * bandwidth. CVSD employs a two level quantizer (one bit) and an + * adaptive algorithm that allows for continuous step size adjustment. + * + * The coder can represent low amplitude signals with accuracy without + * sacrificing performance on large amplitude signals, a trade off that + * occurs in some non-adaptive modulations. + * + * The CVSD encoder effectively provides 8-to-1 compression. More + * specifically, each incoming audio sample is compared to an internal + * reference value. If the input is greater or equal to the reference, + * the encoder outputs a "1" bit. If the input is less than the reference, + * the encoder outputs a "0" bit. The reference value is then updated + * accordingly based on the frequency of outputted "1" or "0" bits. By + * grouping 8 outputs bits together, the encoder essentially produce one + * output byte for every 8 input audio samples. + * + * This encoder requires that input audio samples are 2-byte short signed + * integers. The result bandwidth conversion, therefore, is 16 input bytes + * of raw audio data to 1 output byte of encoded audio data. + * + * The CVSD encoder module must be prefixed by an up-converter to over-sample + * the audio data prior to encoding. The Bluetooth standard specifically + * calls for a 1-to-8 interpolating up-converter. While this reduces the + * overall compression of the codec, this is required so that the encoder + * can accurately compute the slope between adjacent audio samples and + * correctly update its internal reference value. + * + * References: + * + * 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial, + * Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF. + * + * 2. Specification of The Bluetooth System + * Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf. + * + * 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002. + * Bluetooth Voice Simulink® Model, Available: + * http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html + * + */ + class cvsd_encode_sb : public gr_sync_decimator { private: @@ -53,28 +123,35 @@ private: double accum_decay, int K, int J, short pos_accum_max, short neg_accum_max); + //! Member functions required by the encoder/decoder + //! \brief Rounding function specific to CVSD + //! \return the input value rounded to the nearest integer int cvsd_round(double input); + + //! \brief A power function specific to CVSD data formats + //! \return (radix)^power, where radix and power are short integers unsigned int cvsd_pow (short radix, short power); + + //! \brief Sums number of 1's in the input + //! \return the number of 1s in the four bytes of an input unsigned integer unsigned char cvsd_bitwise_sum (unsigned int input); + // Members variables related to the CVSD encoder use to update interal reference value short d_min_step; short d_max_step; double d_step_decay; double d_accum_decay; - //! \brief Size of shift register; the number of output bits remembered in shift register - int d_K; - - //! \brief Number of bits in the shift register that are equal; size of run of 1s, 0s - int d_J; - + int d_K; //!< \brief Size of shift register; the number of output bits remembered in shift register + int d_J; //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s + short d_pos_accum_max; short d_neg_accum_max; - int d_accum; - int d_loop_counter; - unsigned int d_runner; - short d_stepsize; + int d_accum; //!< \brief Current value of internal reference + int d_loop_counter; //!< \brief Current value of the loop counter + unsigned int d_runner; //!< \brief Current value of the shift register + short d_stepsize; //!< \brief Current value of the step sizer public: ~cvsd_encode_sb (); // public destructor |