This block performs CVSD audio encoding. Its design and implementation is modeled after the CVSD encoder/decoder specifications defined in the Bluetooth standard.
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Public Member Functions |
| ~vocoder_cvsd_encode_sb () |
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
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unsigned | decimation () const |
void | set_decimation (unsigned decimation) |
void | forecast (int noutput_items, gr_vector_int &ninput_items_required) |
| Estimate input requirements given output request.
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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
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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.
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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.
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Additional Inherited Members |
| gr_sync_decimator (void) |
| gr_sync_decimator (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature, unsigned decimation) |
| gr_sync_block (void) |
| gr_sync_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature) |
| gr_block (void) |
| gr_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature) |
void | set_fixed_rate (bool fixed_rate) |
void | add_item_tag (unsigned int which_output, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F) |
| Adds a new tag onto the given output buffer.
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void | add_item_tag (unsigned int which_output, const gr_tag_t &tag) |
| Adds a new tag onto the given output buffer.
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void | remove_item_tag (unsigned int which_input, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F) |
| Removes a tag from the given input buffer.
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void | remove_item_tag (unsigned int which_input, const gr_tag_t &tag) |
| Removes a tag from the given input buffer.
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void | get_tags_in_range (std::vector< gr_tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end) |
| Given a [start,end), returns a vector of all tags in the range.
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void | get_tags_in_range (std::vector< gr_tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end, const pmt::pmt_t &key) |
| Given a [start,end), returns a vector of all tags in the range with a given key.
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| gr_basic_block (void) |
| gr_basic_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature) |
| Protected constructor prevents instantiation by non-derived classes.
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void | set_input_signature (gr_io_signature_sptr iosig) |
| may only be called during constructor
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void | set_output_signature (gr_io_signature_sptr iosig) |
| may only be called during constructor
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void | set_color (vcolor color) |
| Allow the flowgraph to set for sorting and partitioning.
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vcolor | color () const |
bool | has_msg_handler (pmt::pmt_t which_port) |
| Tests if there is a handler attached to port which_port .
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virtual void | dispatch_msg (pmt::pmt_t which_port, pmt::pmt_t msg) |
This block performs CVSD audio encoding. 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 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:
- Continuously Variable Slope Delta Modulation (CVSD) A Tutorial, Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
- Specification of The Bluetooth System Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
- 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