GNU Radio 3.6.3.1 C++ API
vocoder_cvsd_decode_bs Class Reference

This block performs CVSD audio decoding. Its design and implementation is modeled after the CVSD encoder/decoder specifications defined in the Bluetooth standard. More...

#include <vocoder_cvsd_decode_bs.h>

Inheritance diagram for vocoder_cvsd_decode_bs:
gr_sync_interpolator gr_sync_block gr_block gr_basic_block gr_msg_accepter gruel::msg_accepter

Public Member Functions

 ~vocoder_cvsd_decode_bs ()
short min_step ()
short max_step ()
double step_decay ()
double accum_decay ()
int K ()
int J ()
short pos_accum_max ()
short neg_accum_max ()
int work (int noutput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
 just like gr_block::general_work, only this arranges to call consume_each for you
- Public Member Functions inherited from gr_sync_interpolator
unsigned interpolation () const
void set_interpolation (unsigned interpolation)
void forecast (int noutput_items, gr_vector_int &ninput_items_required)
 Estimate input requirements given output request.
int general_work (int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
 compute output items from input items
int fixed_rate_ninput_to_noutput (int ninput)
 Given ninput samples, return number of output samples that will be produced. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this.
int fixed_rate_noutput_to_ninput (int noutput)
 Given noutput samples, return number of input samples required to produce noutput. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this.

Friends

VOCODER_API
vocoder_cvsd_decode_bs_sptr 
vocoder_make_cvsd_decode_bs (short min_step, short max_step, double step_decay, double accum_decay, int K, int J, short pos_accum_max, short neg_accum_max)
 Constructor parameters to initialize the CVSD decoder. The default values are modeled after the Bluetooth standard and should not be changed, except by an advanced user.

Additional Inherited Members

- Public Types inherited from gr_block
enum  { WORK_CALLED_PRODUCE = -2, WORK_DONE = -1 }
 Magic return values from general_work. More...
enum  tag_propagation_policy_t { TPP_DONT = 0, TPP_ALL_TO_ALL = 1, TPP_ONE_TO_ONE = 2 }
- Protected Types inherited from gr_basic_block
enum  vcolor { WHITE, GREY, BLACK }
- Protected Member Functions inherited from gr_sync_interpolator
 gr_sync_interpolator (void)
 gr_sync_interpolator (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature, unsigned interpolation)
- Protected Attributes inherited from gr_block
std::vector< long > d_max_output_buffer
std::vector< long > d_min_output_buffer

Detailed Description

This block performs CVSD audio decoding. Its design and implementation is modeled after the CVSD encoder/decoder specifications defined in the Bluetooth standard.

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 decoder effectively provides 1-to-8 decompression. More specifically, for each incoming input bit, the decoder outputs one audio sample. If the input is a "1" bit, the internal reference is increased appropriately and then outputted as the next estimated audio sample. If the input is a "0" bit, the internal reference is decreased appropriately and then likewise outputted as the next estimated audio sample. Grouping 8 input bits together, the encoder essentially produces 8 output audio samples for everyone one input byte.

This decoder requires that output audio samples are 2-byte short signed integers. The result bandwidth conversion, therefore, is 1 byte of encoded audio data to 16 output bytes of raw audio data.

The CVSD decoder module must be post-fixed by a down-converter to under-sample the audio data after decoding. The Bluetooth standard specifically calls for a 8-to-1 decimating down-converter. This is required so that so that output sampling rate equals the original input sampling rate present before the encoder. In all cases, the output down-converter rate must be the inverse of the input up-converter rate before the CVSD encoder.

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

Constructor & Destructor Documentation

vocoder_cvsd_decode_bs::~vocoder_cvsd_decode_bs ( )

Member Function Documentation

double vocoder_cvsd_decode_bs::accum_decay ( )
inline
int vocoder_cvsd_decode_bs::J ( )
inline
int vocoder_cvsd_decode_bs::K ( )
inline
short vocoder_cvsd_decode_bs::max_step ( )
inline
short vocoder_cvsd_decode_bs::min_step ( )
inline
short vocoder_cvsd_decode_bs::neg_accum_max ( )
inline
short vocoder_cvsd_decode_bs::pos_accum_max ( )
inline
double vocoder_cvsd_decode_bs::step_decay ( )
inline
int vocoder_cvsd_decode_bs::work ( int  noutput_items,
gr_vector_const_void_star input_items,
gr_vector_void_star output_items 
)
virtual

just like gr_block::general_work, only this arranges to call consume_each for you

The user must override work to define the signal processing code

Implements gr_sync_block.

Friends And Related Function Documentation

VOCODER_API vocoder_cvsd_decode_bs_sptr vocoder_make_cvsd_decode_bs ( short  min_step,
short  max_step,
double  step_decay,
double  accum_decay,
int  K,
int  J,
short  pos_accum_max,
short  neg_accum_max 
)
friend

Constructor parameters to initialize the CVSD decoder. The default values are modeled after the Bluetooth standard and should not be changed, except by an advanced user.

Parameters
min_stepMinimum step size used to update the internal reference. Default: "10"
max_stepMaximum step size used to update the internal reference. Default: "1280"
step_decayDecay 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)
accum_decayDecay factor applied to the internal reference during every interation of the codec. Default: "0.96875" (i.e. 1-1/32)
K;Size of shift register; the number of output bits remembered by codec (must be less or equal to 32). Default: "32"
J;Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
pos_accum_maxMaximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT)
neg_accum_maxMinimum integer value allowed for the internal reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1)

The documentation for this class was generated from the following file: