diff options
Diffstat (limited to 'util')
| -rw-r--r-- | util/spkmodem_decode/spkmodem-decode.c | 74 |
1 files changed, 71 insertions, 3 deletions
diff --git a/util/spkmodem_decode/spkmodem-decode.c b/util/spkmodem_decode/spkmodem-decode.c index f08b1b52..a621db6d 100644 --- a/util/spkmodem_decode/spkmodem-decode.c +++ b/util/spkmodem_decode/spkmodem-decode.c @@ -80,6 +80,8 @@ /* * Frequency of audio in Hz + * WARNING: if changing, make sure to adjust + * SAMPLES_PER_FRAME accordingly (see maths below) */ #define SAMPLE_RATE 48000 @@ -153,6 +155,19 @@ #define FREQ_DATA_THRESHOLD ((DATA_TONE_THRESHOLD_HZ) / (FRAME_RATE)) /* + * These determine how long the program will wait during + * tone auto-detection, before shifting to defaults. + * + * For tone auto-detection (time waiting for detection) + * NOTE: you could multiply SAMPLE_PER_FRAME instead + * of SAMPLE_RATE in LEARN_SAMPLES, for more granularity. + * Here, 1 * SAMPLE_RATE represents 1 second, which seems + * like a reasonable, conservative default wait time. + */ +#define LEARN_SECONDS 1 +#define LEARN_SAMPLES ((LEARN_SECONDS) * (SAMPLE_RATE)) + +/* * Sample amplitude threshold used to convert the waveform * into a pulse stream. Values near zero are regarded as noise. */ @@ -189,6 +204,12 @@ struct decoder_state { int sep_samples; int sep_min; int sep_max; + + /* for automatic tone detection */ + int freq_min; + int freq_max; + int freq_threshold; + int learn_samples; }; static const char *argv0; @@ -197,6 +218,7 @@ static int host_is_big_endian(void); static void handle_audio(struct decoder_state *st); static int valid_signal(struct decoder_state *st); static void decode_pulse(struct decoder_state *st); +static void auto_detect_tone(struct decoder_state *st); static signed short read_sample(struct decoder_state *st); static int set_ascii_bit(struct decoder_state *st); static void print_char(struct decoder_state *st); @@ -237,6 +259,11 @@ main(int argc, char **argv) break; } + /* fallback in case tone detection fails */ + st.freq_min = 100000; + st.freq_max = 0; + st.freq_threshold = FREQ_DATA_THRESHOLD; + /* * Used for separator calibration */ @@ -405,9 +432,50 @@ decode_pulse(struct decoder_state *st) st->ringpos = ringpos; st->sep_pos = sep_pos; + /* + * Attempt to auto-detect spkmodem tone + */ + auto_detect_tone(st); + st->sample_count++; } +/* + * Observe signal for LEARN_SAMPLES samples (e.g. 1 second). + * The exact amount of time is determined by LEARN_SAMPLES + * divided by SAMPLE_RATE, logically. For example, if + * LEARN_SAMPLES were half of the SAMPLE_RATE, this + * corresponds to roughly 500ms before timeout. + * + * to guess the correct timing. If it fails, + * fall back to known good values. + */ +static void +auto_detect_tone(struct decoder_state *st) +{ + if (st->learn_samples >= LEARN_SAMPLES) + return; + + if (st->freq_data > 0) { + if (st->freq_data < st->freq_min) + st->freq_min = st->freq_data; + + if (st->freq_data > st->freq_max) + st->freq_max = st->freq_data; + } + + st->learn_samples++; + + if (st->learn_samples == LEARN_SAMPLES) { + st->freq_threshold = + (st->freq_min + st->freq_max) / 2; + + if (st->debug) + printf("auto threshold: %dHz\n", + st->freq_threshold * FRAME_RATE); + } +} + static signed short read_sample(struct decoder_state *st) { @@ -452,7 +520,7 @@ set_ascii_bit(struct decoder_state *st) { if (st->debug) print_stats(st); - if (st->freq_data < FREQ_DATA_THRESHOLD) + if (st->freq_data < st->freq_threshold) st->ascii |= (1 << st->ascii_bit); st->ascii_bit--; @@ -484,7 +552,7 @@ print_stats(struct decoder_state *st) printf("%d %d %d data=%dHz sep=%dHz(min %dHz %dHz)\n", st->freq_data, st->freq_separator, - FREQ_DATA_THRESHOLD, + st->freq_threshold, data_hz, sep_hz, sep_hz_min, @@ -495,7 +563,7 @@ print_stats(struct decoder_state *st) printf("%d %d %d @%ld data=%dHz sep=%dHz(min %dHz %dHz)\n", st->freq_data, st->freq_separator, - FREQ_DATA_THRESHOLD, + st->freq_threshold, pos - SAMPLE_OFFSET, data_hz, sep_hz, |