dtmf.h

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00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * dtmf.h - 
00005  *
00006  * Written by Steve Underwood <steveu@coppice.org>
00007  *
00008  * Copyright (C) 2001, 2005 Steve Underwood
00009  *
00010  * All rights reserved.
00011  *
00012  * This program is free software; you can redistribute it and/or modify
00013  * it under the terms of the GNU General Public License version 2, as
00014  * published by the Free Software Foundation.
00015  *
00016  * This program is distributed in the hope that it will be useful,
00017  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00018  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00019  * GNU General Public License for more details.
00020  *
00021  * You should have received a copy of the GNU General Public License
00022  * along with this program; if not, write to the Free Software
00023  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00024  *
00025  * $Id: dtmf.h,v 1.11 2007/05/19 18:01:47 steveu Exp $
00026  */
00027 
00028 #if !defined(_SPANDSP_DTMF_H_)
00029 #define _SPANDSP_DTMF_H_
00030 
00031 /*! \page dtmf_rx_page DTMF receiver
00032 \section dtmf_rx_page_sec_1 What does it do?
00033 The DTMF receiver detects the standard DTMF digits. It is compliant with
00034 ITU-T Q.23, ITU-T Q.24, and the local DTMF specifications of most administrations.
00035 Its passes the test suites. It also scores *very* well on the standard
00036 talk-off tests. 
00037 
00038 The current design uses floating point extensively. It is not tolerant of DC.
00039 It is expected that a DC restore stage will be placed before the DTMF detector.
00040 Unless the dial tone filter is switched on, the detector has poor tolerance
00041 of dial tone. Whether this matter depends on your application. If you are using
00042 the detector in an IVR application you will need proper echo cancellation to
00043 get good performance in the presence of speech prompts, so dial tone will not
00044 exist. If you do need good dial tone tolerance, a dial tone filter can be
00045 enabled in the detector.
00046 
00047 \section dtmf_rx_page_sec_2 How does it work?
00048 Like most other DSP based DTMF detector's, this one uses the Goertzel algorithm
00049 to look for the DTMF tones. What makes each detector design different is just how
00050 that algorithm is used.
00051 
00052 Basic DTMF specs:
00053     - Minimum tone on = 40ms
00054     - Minimum tone off = 50ms
00055     - Maximum digit rate = 10 per second
00056     - Normal twist <= 8dB accepted
00057     - Reverse twist <= 4dB accepted
00058     - S/N >= 15dB will detect OK
00059     - Attenuation <= 26dB will detect OK
00060     - Frequency tolerance +- 1.5% will detect, +-3.5% will reject
00061 
00062 TODO:
00063 */
00064 
00065 /*! \page dtmf_tx_page DTMF tone generation
00066 \section dtmf_tx_page_sec_1 What does it do?
00067 
00068 The DTMF tone generation module provides for the generation of the
00069 repertoire of 16 DTMF dual tones. 
00070 
00071 \section dtmf_tx_page_sec_2 How does it work?
00072 */
00073 
00074 #define MAX_DTMF_DIGITS 128
00075 
00076 typedef void (*dtmf_rx_callback_t)(void *user_data, const char *digits, int len);
00077 
00078 /*!
00079     DTMF generator state descriptor. This defines the state of a single
00080     working instance of a DTMF generator.
00081 */
00082 typedef struct
00083 {
00084     tone_gen_descriptor_t *tone_descriptors;
00085     tone_gen_state_t tones;
00086     int current_sample;
00087     /* The queue structure MUST be followed immediately by the buffer */
00088     queue_state_t queue;
00089     char digits[MAX_DTMF_DIGITS + 1];
00090 } dtmf_tx_state_t;
00091 
00092 /*!
00093     DTMF digit detector descriptor.
00094 */
00095 typedef struct
00096 {
00097     /*! Optional callback funcion to deliver received digits. */
00098     dtmf_rx_callback_t callback;
00099     /*! An opaque pointer passed to the callback function. */
00100     void *callback_data;
00101     /*! Optional callback funcion to deliver real time digit state changes. */
00102     tone_report_func_t realtime_callback;
00103     /*! An opaque pointer passed to the real time callback function. */
00104     void *realtime_callback_data;
00105     /*! TRUE if dialtone should be filtered before processing */
00106     int filter_dialtone;
00107     /*! Maximum acceptable "normal" (lower bigger than higher) twist ratio */
00108     float normal_twist;
00109     /*! Maximum acceptable "reverse" (higher bigger than lower) twist ratio */
00110     float reverse_twist;
00111 
00112     /*! 350Hz filter state for the optional dialtone filter */
00113     float z350_1;
00114     float z350_2;
00115     /*! 440Hz filter state for the optional dialtone filter */
00116     float z440_1;
00117     float z440_2;
00118 
00119     /*! Tone detector working states */
00120     goertzel_state_t row_out[4];
00121     goertzel_state_t col_out[4];
00122     /*! The accumlating total energy on the same period over which the Goertzels work. */
00123     float energy;
00124     /*! The result of the last tone analysis. */
00125     uint8_t last_hit;
00126     /*! The confirmed digit we are currently receiving */
00127     uint8_t in_digit;
00128     /*! The current sample number within a processing block. */
00129     int current_sample;
00130 
00131     /*! The number of digits which have been lost due to buffer overflows. */
00132     int lost_digits;
00133     /*! The number of digits currently in the digit buffer. */
00134     int current_digits;
00135     /*! The received digits buffer. This is a NULL terminated string. */
00136     char digits[MAX_DTMF_DIGITS + 1];
00137 } dtmf_rx_state_t;
00138 
00139 #if defined(__cplusplus)
00140 extern "C"
00141 {
00142 #endif
00143 
00144 /*! \brief Generate a buffer of DTMF tones.
00145     \param s The DTMF generator context.
00146     \param amp The buffer for the generated signal.
00147     \param max_samples The required number of generated samples.
00148     \return The number of samples actually generated. This may be less than 
00149             max_samples if the input buffer empties. */
00150 int dtmf_tx(dtmf_tx_state_t *s, int16_t amp[], int max_samples);
00151 
00152 /*! \brief Put a string of digits in a DTMF generator's input buffer.
00153     \param s The DTMF generator context.
00154     \param digits The string of digits to be added.
00155     \return The number of digits actually added. This may be less than the
00156             length of the digit string, if the buffer fills up. */
00157 size_t dtmf_tx_put(dtmf_tx_state_t *s, const char *digits);
00158 
00159 /*! \brief Initialise a DTMF tone generator context.
00160     \param s The DTMF generator context.
00161     \return A pointer to the DTMF generator context. */
00162 dtmf_tx_state_t *dtmf_tx_init(dtmf_tx_state_t *s);
00163 
00164 /*! Set a optional realtime callback for a DTMF receiver context. This function
00165     is called immediately a confirmed state change occurs in the received DTMF. It
00166     is called with the ASCII value for a DTMF tone pair, or zero to indicate no tone
00167     is being received.
00168     \brief Set a realtime callback for a DTMF receiver context.
00169     \param s The DTMF receiver context.
00170     \param callback Callback routine used to report the start and end of digits.
00171     \param user_data An opaque pointer which is associated with the context,
00172            and supplied in callbacks. */
00173 void dtmf_rx_set_realtime_callback(dtmf_rx_state_t *s,
00174                                    tone_report_func_t callback,
00175                                    void *user_data);
00176 
00177 /*! \brief Adjust a DTMF receiver context.
00178     \param s The DTMF receiver context.
00179     \param filter_dialtone TRUE to enable filtering of dialtone, FALSE
00180            to disable, < 0 to leave unchanged.
00181     \param twist Acceptable twist, in dB. < 0 to leave unchanged.
00182     \param reverse_twist Acceptable reverse twist, in dB. < 0 to leave unchanged. */
00183 void dtmf_rx_parms(dtmf_rx_state_t *s, int filter_dialtone, int twist, int reverse_twist);
00184 
00185 /*! Process a block of received DTMF audio samples.
00186     \brief Process a block of received DTMF audio samples.
00187     \param s The DTMF receiver context.
00188     \param amp The audio sample buffer.
00189     \param samples The number of samples in the buffer.
00190     \return The number of samples unprocessed. */
00191 int dtmf_rx(dtmf_rx_state_t *s, const int16_t amp[], int samples);
00192 
00193 /*! \brief Get a string of digits from a DTMF receiver's output buffer.
00194     \param s The DTMF receiver context.
00195     \param digits The buffer for the received digits.
00196     \param max The maximum  number of digits to be returned,
00197     \return The number of digits actually returned. */
00198 size_t dtmf_rx_get(dtmf_rx_state_t *s, char *digits, int max);
00199 
00200 /*! \brief Initialise a DTMF receiver context.
00201     \param s The DTMF receiver context.
00202     \param callback An optional callback routine, used to report received digits. If
00203            no callback routine is set, digits may be collected, using the dtmf_rx_get()
00204            function.
00205     \param user_data An opaque pointer which is associated with the context,
00206            and supplied in callbacks.
00207     \return A pointer to the DTMF receiver context. */
00208 dtmf_rx_state_t *dtmf_rx_init(dtmf_rx_state_t *s,
00209                               dtmf_rx_callback_t callback,
00210                               void *user_data);
00211 
00212 #if defined(__cplusplus)
00213 }
00214 #endif
00215 
00216 #endif
00217 /*- End of file ------------------------------------------------------------*/

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