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>
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 | |
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. | |
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_step Minimum step size used to update the internal reference. Default: "10" max_step Maximum step size used to update the internal reference. Default: "1280" 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) accum_decay Decay 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_max Maximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT) neg_accum_max Minimum 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:
