65 lines
2.1 KiB
C
65 lines
2.1 KiB
C
/* Sample definition
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*
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* (C) 2017 by Andreas Eversberg <jolly@eversberg.eu>
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* All Rights Reserved
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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#include "sample.h"
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/*
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* A regular voice conversation takes place at this factor below the full range
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* of 16 bits signed value:
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*/
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static double int_16_speech_level = SPEECH_LEVEL * 0.7079; /* 16 dBm below dBm0, which is about 3dBm below full 16 bit range */
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/* A sample_t is a value that has virtually infinite precision but will also
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* support high numbers. 'double' or 'float' types are sufficient.
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*
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* When using sample_t inside signal processing of each base station, the
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* level of +- 1 is relative to the normal speach evenlope.
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*
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* When converting sample_t to int16_t, the level of +- 1 is reduced by factor.
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* This way the speech may be louder before clipping happens.
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*
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* When using sample_t to modulate (SDR or sound card), the level is changed,
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* so it represents the frequency deviation in Hz. The deviation of speech
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* envelope is network dependant.
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*/
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void samples_to_int16(int16_t *spl, sample_t *samples, int length)
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{
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int32_t value;
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while (length--) {
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value = *samples++ * int_16_speech_level * 32768.0;
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if (value > 32767.0)
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*spl++ = 32767;
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else if (value < -32767.0)
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*spl++ = -32767;
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else
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*spl++ = (uint16_t)value;
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}
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}
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void int16_to_samples(sample_t *samples, int16_t *spl, int length)
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{
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while (length--) {
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*samples++ = (double)(*spl++) / 32767.0 / int_16_speech_level;
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}
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}
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