From e5d55b64f753e419fcfa48b5b8355c9d401589e3 Mon Sep 17 00:00:00 2001 From: Andreas Eversberg Date: Wed, 7 Oct 2009 18:52:04 +0200 Subject: [PATCH] Don't detect tones for SS5, if the minimum noise level is not reached. This reduces CPU load on idle channels. modified: ss5_decode.c --- ss5_decode.c | 51 +++++++++++++++++++++++++++------------------------ 1 file changed, 27 insertions(+), 24 deletions(-) diff --git a/ss5_decode.c b/ss5_decode.c index 0a00a6f..35e2664 100644 --- a/ss5_decode.c +++ b/ss5_decode.c @@ -18,8 +18,9 @@ #define NCOEFF 8 /* number of frequencies to be analyzed */ -#define MIN_DB 0.01995262 /* -17 db */ -#define DIFF_DB 0.2 // 0.31622777 /* -5 db */ +#define TONE_MIN_DB 0.01995262 /* -17 db */ +#define TONE_DIFF_DB 0.2 // 0.31622777 /* -5 db */ +#define NOISE_MIN_DB (TONE_MIN_DB / 2) /* noise must be higher than the minimum of two tones */ #define SNR 1.3 /* noise may not exceed signal by that factor */ /* For DTMF recognition: @@ -65,6 +66,22 @@ char ss5_decode(unsigned char *data, int len) for (i = 0; i < len; i++) buf[i] = audio_law_to_s32[*data++]; + /* now we do noise level calculation */ + low = 32767; + high = -32768; + for (n = 0; n < len; n++) { + sk = buf[n]; + if (sk < low) + low = sk; + if (sk > high) + high = sk; + } + noise = ((double)(high-low) / 65536.0); + + /* check for minimum noise, or tone detection will not be necessary */ + if (noise < NOISE_MIN_DB) + return digit; + /* now we have a full buffer of signed long samples - we do goertzel */ for (k = 0; k < NCOEFF; k++) { sk = 0; @@ -88,18 +105,6 @@ char ss5_decode(unsigned char *data, int len) ) / len / 62; /* level of 1 is 0 db*/ } - /* now we do noise level calculation */ - low = 32767; - high = -32768; - for (n = 0; n < len; n++) { - sk = buf[n]; - if (sk < low) - low = sk; - if (sk > high) - high = sk; - } - noise = ((double)(high-low) / 65536.0); - /* find the two loudest frequencies + one less lower frequency to detect noise */ power = 0.0; for (i = 0; i < NCOEFF; i++) { @@ -118,15 +123,15 @@ char ss5_decode(unsigned char *data, int len) snr = 0; /* check one frequency */ - if (result[f1] > MIN_DB /* must be at least -17 db */ + if (result[f1] > TONE_MIN_DB /* must be at least -17 db */ && result[f1]*SNR > noise) { /* */ digit = decode_one[f1]; if (digit != ' ') snr = result[f1] / noise; } /* check two frequencies */ - if (result[f1] > MIN_DB && result[f2] > MIN_DB /* must be at lease -17 db */ - && result[f1]*DIFF_DB <= result[f2] /* f2 must be not less than 5 db below f1 */ + if (result[f1] > TONE_MIN_DB && result[f2] > TONE_MIN_DB /* must be at lease -17 db */ + && result[f1]*TONE_DIFF_DB <= result[f2] /* f2 must be not less than 5 db below f1 */ && (result[f1]+result[f2])*SNR > noise) { /* */ digit = decode_two[f1][f2]; if (digit != ' ') @@ -135,13 +140,11 @@ char ss5_decode(unsigned char *data, int len) /* debug powers */ #ifdef DEBUG_LEVELS - if (noise > 0.2) { - for (i = 0; i < NCOEFF; i++) - printf("%d:%3d %c ", i, (int)(result[i]*100), (f1==i || f2==i)?'*':' '); - printf("N:%3d digit:%c snr=%3d\n", (int)(noise*100), digit, (int)(snr*100)); - if (result[f1]*DIFF_DB <= result[f2]) /* f2 must be not less than 5 db below f1 */ - printf("jo!"); - } + for (i = 0; i < NCOEFF; i++) + printf("%d:%3d %c ", i, (int)(result[i]*100), (f1==i || f2==i)?'*':' '); + printf("N:%3d digit:%c snr=%3d\n", (int)(noise*100), digit, (int)(snr*100)); +// if (result[f1]*TONE_DIFF_DB <= result[f2]) /* f2 must be not less than 5 db below f1 */ +// printf("jo!"); #endif return digit; -- 2.13.6