[PATCH] (Was: i4l dtmf errors)

Wolfgang Fritz (wolfgang.fritz@gmx.net)
Mon, 16 Dec 2002 18:44:58 +0100


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<veröffentlicht & per Mail versendet>

Kai Germaschewski wrote:

> On Sat, 14 Dec 2002, Wolfgang Fritz wrote:
>
>> > it seems isdn4linux detects DTMF tones from normal speach. This is
>> > rather annoying when using i4l for voice with Asterisk.org. This is
>> > tested on all recent kernels
>>
>> The DTMF detection is broken since kernel 2.0.x. I have a patch for a
>> 2.2 kernel which may manually be applied 2.4 kernels with some manual
>> work. It fixes an overflow problem in the goertzel algorithm (which
>> does the basic tone detection) and changes the algorithm to detect
>> the DTMF pairs. If interested, I can try to recover that patch.
>
> If you dig out that patch and submit it (to me), I'm pretty sure
> there's a good chance of it going into the official kernel. ISTR there
> was talk about that earlier, but nothing ever happened.
>
> --Kai
>

Here is the patch against 2.4.20.

Wolfgang
>
> -
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diff -urN -X dontdiff linux-2.4.20/drivers/isdn/isdn_audio.c linux-2.4.20.mod/drivers/isdn/isdn_audio.c
--- linux-2.4.20/drivers/isdn/isdn_audio.c Mon Feb 25 20:37:58 2002
+++ linux-2.4.20.mod/drivers/isdn/isdn_audio.c Mon Dec 16 17:45:39 2002
@@ -169,39 +169,19 @@
0x8a, 0x8a, 0x6a, 0x6a, 0xea, 0xea, 0x2a, 0x2a
};

-#define NCOEFF 16 /* number of frequencies to be analyzed */
-#define DTMF_TRESH 25000 /* above this is dtmf */
+#define NCOEFF 8 /* number of frequencies to be analyzed */
+#define DTMF_TRESH 4000 /* above this is dtmf */
#define SILENCE_TRESH 200 /* below this is silence */
-#define H2_TRESH 20000 /* 2nd harmonic */
#define AMP_BITS 9 /* bits per sample, reduced to avoid overflow */
#define LOGRP 0
#define HIGRP 1

-typedef struct {
- int grp; /* low/high group */
- int k; /* k */
- int k2; /* k fuer 2. harmonic */
-} dtmf_t;
-
/* For DTMF recognition:
* 2 * cos(2 * PI * k / N) precalculated for all k
*/
static int cos2pik[NCOEFF] =
{
- 55812, 29528, 53603, 24032, 51193, 14443, 48590, 6517,
- 38113, -21204, 33057, -32186, 25889, -45081, 18332, -55279
-};
-
-static dtmf_t dtmf_tones[8] =
-{
- {LOGRP, 0, 1}, /* 697 Hz */
- {LOGRP, 2, 3}, /* 770 Hz */
- {LOGRP, 4, 5}, /* 852 Hz */
- {LOGRP, 6, 7}, /* 941 Hz */
- {HIGRP, 8, 9}, /* 1209 Hz */
- {HIGRP, 10, 11}, /* 1336 Hz */
- {HIGRP, 12, 13}, /* 1477 Hz */
- {HIGRP, 14, 15} /* 1633 Hz */
+ 55813, 53604, 51193, 48591, 38114, 33057, 25889, 18332
};

static char dtmf_matrix[4][4] =
@@ -499,6 +479,18 @@
sk2 = sk1;
sk1 = sk;
}
+ /* Avoid overflows */
+ sk >>= 1;
+ sk2 >>= 1;
+ /* compute |X(k)|**2 */
+ /* report overflows. This should not happen. */
+ /* Comment this out if desired */
+ if (sk < -32768 || sk > 32767)
+ printk(KERN_DEBUG
+ "isdn_audio: dtmf goertzel overflow, sk=%d\n", sk);
+ if (sk2 < -32768 || sk2 > 32767)
+ printk(KERN_DEBUG
+ "isdn_audio: dtmf goertzel overflow, sk2=%d\n", sk2);
result[k] =
((sk * sk) >> AMP_BITS) -
((((cos2pik[k] * sk) >> 15) * sk2) >> AMP_BITS) +
@@ -522,28 +514,58 @@
int grp[2];
char what;
char *p;
+ int thresh;

while ((skb = skb_dequeue(&info->dtmf_queue))) {
result = (int *) skb->data;
s = info->dtmf_state;
- grp[LOGRP] = grp[HIGRP] = -2;
+ grp[LOGRP] = grp[HIGRP] = -1;
silence = 0;
- for (i = 0; i < 8; i++) {
- if ((result[dtmf_tones[i].k] > DTMF_TRESH) &&
- (result[dtmf_tones[i].k2] < H2_TRESH))
- grp[dtmf_tones[i].grp] = (grp[dtmf_tones[i].grp] == -2) ? i : -1;
- else if ((result[dtmf_tones[i].k] < SILENCE_TRESH) &&
- (result[dtmf_tones[i].k2] < SILENCE_TRESH))
+ thresh = 0;
+ for (i = 0; i < NCOEFF; i++) {
+ if (result[i] > DTMF_TRESH) {
+ if (result[i] > thresh)
+ thresh = result[i];
+ }
+ else if (result[i] < SILENCE_TRESH)
silence++;
}
- if (silence == 8)
+ if (silence == NCOEFF)
what = ' ';
else {
- if ((grp[LOGRP] >= 0) && (grp[HIGRP] >= 0)) {
- what = dtmf_matrix[grp[LOGRP]][grp[HIGRP] - 4];
- if (s->last != ' ' && s->last != '.')
- s->last = what; /* min. 1 non-DTMF between DTMF */
- } else
+ if (thresh > 0) {
+ thresh = thresh >> 4; /* touchtones must match within 12 dB */
+ for (i = 0; i < NCOEFF; i++) {
+ if (result[i] < thresh)
+ continue; /* ignore */
+ /* good level found. This is allowed only one time per group */
+ if (i < NCOEFF / 2) {
+ /* lowgroup*/
+ if (grp[LOGRP] >= 0) {
+ // Bad. Another tone found. */
+ grp[LOGRP] = -1;
+ break;
+ }
+ else
+ grp[LOGRP] = i;
+ }
+ else { /* higroup */
+ if (grp[HIGRP] >= 0) { // Bad. Another tone found. */
+ grp[HIGRP] = -1;
+ break;
+ }
+ else
+ grp[HIGRP] = i - NCOEFF/2;
+ }
+ }
+ if ((grp[LOGRP] >= 0) && (grp[HIGRP] >= 0)) {
+ what = dtmf_matrix[grp[LOGRP]][grp[HIGRP]];
+ if (s->last != ' ' && s->last != '.')
+ s->last = what; /* min. 1 non-DTMF between DTMF */
+ } else
+ what = '.';
+ }
+ else
what = '.';
}
if ((what != s->last) && (what != ' ') && (what != '.')) {
diff -urN -X dontdiff linux-2.4.20/drivers/isdn/isdn_audio.h linux-2.4.20.mod/drivers/isdn/isdn_audio.h
--- linux-2.4.20/drivers/isdn/isdn_audio.h Fri Dec 21 18:41:54 2001
+++ linux-2.4.20.mod/drivers/isdn/isdn_audio.h Mon Dec 16 17:42:32 2002
@@ -20,6 +20,7 @@

typedef struct dtmf_state {
char last;
+ char llast;
int idx;
int buf[DTMF_NPOINTS];
} dtmf_state;

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