Steve also has some nice notes on echo cancellers in echo.h
-
References:
[1] Ochiai, Areseki, and Ogihara, "Echo Canceller with Two Echo
Mark, Pawel, and Pavel.
*/
-#include <linux/kernel.h> /* We're doing kernel work */
+#include <linux/kernel.h> /* We're doing kernel work */
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
-#define malloc(a) kmalloc((a), GFP_KERNEL)
-#define free(a) kfree(a)
#include "bit_operations.h"
#include "echo.h"
#define MIN_TX_POWER_FOR_ADAPTION 64
#define MIN_RX_POWER_FOR_ADAPTION 64
-#define DTD_HANGOVER 600 /* 600 samples, or 75ms */
-#define DC_LOG2BETA 3 /* log2() of DC filter Beta */
+#define DTD_HANGOVER 600 /* 600 samples, or 75ms */
+#define DC_LOG2BETA 3 /* log2() of DC filter Beta */
/*-----------------------------------------------------------------------*\
FUNCTIONS
/* adapting coeffs using the traditional stochastic descent (N)LMS algorithm */
-
-#ifdef __BLACKFIN_ASM__
-static void __inline__ lms_adapt_bg(struct oslec_state *ec, int clean, int shift)
+#ifdef __bfin__
+static void __inline__ lms_adapt_bg(struct oslec_state *ec, int clean,
+ int shift)
{
- int i, j;
- int offset1;
- int offset2;
- int factor;
- int exp;
- int16_t *phist;
- int n;
-
- if (shift > 0)
- factor = clean << shift;
- else
- factor = clean >> -shift;
-
- /* Update the FIR taps */
-
- offset2 = ec->curr_pos;
- offset1 = ec->taps - offset2;
- phist = &ec->fir_state_bg.history[offset2];
-
- /* st: and en: help us locate the assembler in echo.s */
-
- //asm("st:");
- n = ec->taps;
- for (i = 0, j = offset2; i < n; i++, j++)
- {
- exp = *phist++ * factor;
- ec->fir_taps16[1][i] += (int16_t) ((exp+(1<<14)) >> 15);
- }
- //asm("en:");
-
- /* Note the asm for the inner loop above generated by Blackfin gcc
- 4.1.1 is pretty good (note even parallel instructions used):
-
- R0 = W [P0++] (X);
- R0 *= R2;
- R0 = R0 + R3 (NS) ||
- R1 = W [P1] (X) ||
- nop;
- R0 >>>= 15;
- R0 = R0 + R1;
- W [P1++] = R0;
-
- A block based update algorithm would be much faster but the
- above can't be improved on much. Every instruction saved in
- the loop above is 2 MIPs/ch! The for loop above is where the
- Blackfin spends most of it's time - about 17 MIPs/ch measured
- with speedtest.c with 256 taps (32ms). Write-back and
- Write-through cache gave about the same performance.
- */
+ int i, j;
+ int offset1;
+ int offset2;
+ int factor;
+ int exp;
+ int16_t *phist;
+ int n;
+
+ if (shift > 0)
+ factor = clean << shift;
+ else
+ factor = clean >> -shift;
+
+ /* Update the FIR taps */
+
+ offset2 = ec->curr_pos;
+ offset1 = ec->taps - offset2;
+ phist = &ec->fir_state_bg.history[offset2];
+
+ /* st: and en: help us locate the assembler in echo.s */
+
+ //asm("st:");
+ n = ec->taps;
+ for (i = 0, j = offset2; i < n; i++, j++) {
+ exp = *phist++ * factor;
+ ec->fir_taps16[1][i] += (int16_t) ((exp + (1 << 14)) >> 15);
+ }
+ //asm("en:");
+
+ /* Note the asm for the inner loop above generated by Blackfin gcc
+ 4.1.1 is pretty good (note even parallel instructions used):
+
+ R0 = W [P0++] (X);
+ R0 *= R2;
+ R0 = R0 + R3 (NS) ||
+ R1 = W [P1] (X) ||
+ nop;
+ R0 >>>= 15;
+ R0 = R0 + R1;
+ W [P1++] = R0;
+
+ A block based update algorithm would be much faster but the
+ above can't be improved on much. Every instruction saved in
+ the loop above is 2 MIPs/ch! The for loop above is where the
+ Blackfin spends most of it's time - about 17 MIPs/ch measured
+ with speedtest.c with 256 taps (32ms). Write-back and
+ Write-through cache gave about the same performance.
+ */
}
/*
*/
#else
-static __inline__ void lms_adapt_bg(struct oslec_state *ec, int clean, int shift)
+static __inline__ void lms_adapt_bg(struct oslec_state *ec, int clean,
+ int shift)
{
- int i;
-
- int offset1;
- int offset2;
- int factor;
- int exp;
-
- if (shift > 0)
- factor = clean << shift;
- else
- factor = clean >> -shift;
-
- /* Update the FIR taps */
-
- offset2 = ec->curr_pos;
- offset1 = ec->taps - offset2;
-
- for (i = ec->taps - 1; i >= offset1; i--)
- {
- exp = (ec->fir_state_bg.history[i - offset1]*factor);
- ec->fir_taps16[1][i] += (int16_t) ((exp+(1<<14)) >> 15);
- }
- for ( ; i >= 0; i--)
- {
- exp = (ec->fir_state_bg.history[i + offset2]*factor);
- ec->fir_taps16[1][i] += (int16_t) ((exp+(1<<14)) >> 15);
- }
+ int i;
+
+ int offset1;
+ int offset2;
+ int factor;
+ int exp;
+
+ if (shift > 0)
+ factor = clean << shift;
+ else
+ factor = clean >> -shift;
+
+ /* Update the FIR taps */
+
+ offset2 = ec->curr_pos;
+ offset1 = ec->taps - offset2;
+
+ for (i = ec->taps - 1; i >= offset1; i--) {
+ exp = (ec->fir_state_bg.history[i - offset1] * factor);
+ ec->fir_taps16[1][i] += (int16_t) ((exp + (1 << 14)) >> 15);
+ }
+ for (; i >= 0; i--) {
+ exp = (ec->fir_state_bg.history[i + offset2] * factor);
+ ec->fir_taps16[1][i] += (int16_t) ((exp + (1 << 14)) >> 15);
+ }
}
#endif
-/*- End of function --------------------------------------------------------*/
-
struct oslec_state *oslec_create(int len, int adaption_mode)
{
- struct oslec_state *ec;
- int i;
- int j;
-
- ec = kmalloc(sizeof(*ec), GFP_KERNEL);
- if (ec == NULL)
- return NULL;
- memset(ec, 0, sizeof(*ec));
-
- ec->taps = len;
- ec->log2taps = top_bit(len);
- ec->curr_pos = ec->taps - 1;
-
- for (i = 0; i < 2; i++)
- {
- if ((ec->fir_taps16[i] = (int16_t *) malloc((ec->taps)*sizeof(int16_t))) == NULL)
- {
- for (j = 0; j < i; j++)
- kfree(ec->fir_taps16[j]);
- kfree(ec);
- return NULL;
- }
- memset(ec->fir_taps16[i], 0, (ec->taps)*sizeof(int16_t));
- }
-
- fir16_create(&ec->fir_state,
- ec->fir_taps16[0],
- ec->taps);
- fir16_create(&ec->fir_state_bg,
- ec->fir_taps16[1],
- ec->taps);
-
- for(i=0; i<5; i++) {
- ec->xvtx[i] = ec->yvtx[i] = ec->xvrx[i] = ec->yvrx[i] = 0;
- }
-
- ec->cng_level = 1000;
- oslec_adaption_mode(ec, adaption_mode);
-
- ec->snapshot = (int16_t*)malloc(ec->taps*sizeof(int16_t));
- memset(ec->snapshot, 0, sizeof(int16_t)*ec->taps);
-
- ec->cond_met = 0;
- ec->Pstates = 0;
- ec->Ltxacc = ec->Lrxacc = ec->Lcleanacc = ec->Lclean_bgacc = 0;
- ec->Ltx = ec->Lrx = ec->Lclean = ec->Lclean_bg = 0;
- ec->tx_1 = ec->tx_2 = ec->rx_1 = ec->rx_2 = 0;
- ec->Lbgn = ec->Lbgn_acc = 0;
- ec->Lbgn_upper = 200;
- ec->Lbgn_upper_acc = ec->Lbgn_upper << 13;
-
- return ec;
+ struct oslec_state *ec;
+ int i;
+
+ ec = kzalloc(sizeof(*ec), GFP_KERNEL);
+ if (!ec)
+ return NULL;
+
+ ec->taps = len;
+ ec->log2taps = top_bit(len);
+ ec->curr_pos = ec->taps - 1;
+
+ for (i = 0; i < 2; i++) {
+ ec->fir_taps16[i] =
+ kcalloc(ec->taps, sizeof(int16_t), GFP_KERNEL);
+ if (!ec->fir_taps16[i])
+ goto error_oom;
+ }
+
+ fir16_create(&ec->fir_state, ec->fir_taps16[0], ec->taps);
+ fir16_create(&ec->fir_state_bg, ec->fir_taps16[1], ec->taps);
+
+ for (i = 0; i < 5; i++) {
+ ec->xvtx[i] = ec->yvtx[i] = ec->xvrx[i] = ec->yvrx[i] = 0;
+ }
+
+ ec->cng_level = 1000;
+ oslec_adaption_mode(ec, adaption_mode);
+
+ ec->snapshot = kcalloc(ec->taps, sizeof(int16_t), GFP_KERNEL);
+ if (!ec->snapshot)
+ goto error_oom;
+
+ ec->cond_met = 0;
+ ec->Pstates = 0;
+ ec->Ltxacc = ec->Lrxacc = ec->Lcleanacc = ec->Lclean_bgacc = 0;
+ ec->Ltx = ec->Lrx = ec->Lclean = ec->Lclean_bg = 0;
+ ec->tx_1 = ec->tx_2 = ec->rx_1 = ec->rx_2 = 0;
+ ec->Lbgn = ec->Lbgn_acc = 0;
+ ec->Lbgn_upper = 200;
+ ec->Lbgn_upper_acc = ec->Lbgn_upper << 13;
+
+ return ec;
+
+ error_oom:
+ for (i = 0; i < 2; i++)
+ kfree(ec->fir_taps16[i]);
+
+ kfree(ec);
+ return NULL;
}
+
EXPORT_SYMBOL_GPL(oslec_create);
-/*- End of function --------------------------------------------------------*/
void oslec_free(struct oslec_state *ec)
{
fir16_free(&ec->fir_state);
fir16_free(&ec->fir_state_bg);
- for (i = 0; i < 2; i++)
+ for (i = 0; i < 2; i++)
kfree(ec->fir_taps16[i]);
kfree(ec->snapshot);
kfree(ec);
}
+
EXPORT_SYMBOL_GPL(oslec_free);
-/*- End of function --------------------------------------------------------*/
void oslec_adaption_mode(struct oslec_state *ec, int adaption_mode)
{
- ec->adaption_mode = adaption_mode;
+ ec->adaption_mode = adaption_mode;
}
+
EXPORT_SYMBOL_GPL(oslec_adaption_mode);
-/*- End of function --------------------------------------------------------*/
void oslec_flush(struct oslec_state *ec)
{
- int i;
+ int i;
- ec->Ltxacc = ec->Lrxacc = ec->Lcleanacc = ec->Lclean_bgacc = 0;
- ec->Ltx = ec->Lrx = ec->Lclean = ec->Lclean_bg = 0;
- ec->tx_1 = ec->tx_2 = ec->rx_1 = ec->rx_2 = 0;
+ ec->Ltxacc = ec->Lrxacc = ec->Lcleanacc = ec->Lclean_bgacc = 0;
+ ec->Ltx = ec->Lrx = ec->Lclean = ec->Lclean_bg = 0;
+ ec->tx_1 = ec->tx_2 = ec->rx_1 = ec->rx_2 = 0;
- ec->Lbgn = ec->Lbgn_acc = 0;
- ec->Lbgn_upper = 200;
- ec->Lbgn_upper_acc = ec->Lbgn_upper << 13;
+ ec->Lbgn = ec->Lbgn_acc = 0;
+ ec->Lbgn_upper = 200;
+ ec->Lbgn_upper_acc = ec->Lbgn_upper << 13;
- ec->nonupdate_dwell = 0;
+ ec->nonupdate_dwell = 0;
- fir16_flush(&ec->fir_state);
- fir16_flush(&ec->fir_state_bg);
- ec->fir_state.curr_pos = ec->taps - 1;
- ec->fir_state_bg.curr_pos = ec->taps - 1;
- for (i = 0; i < 2; i++)
- memset(ec->fir_taps16[i], 0, ec->taps*sizeof(int16_t));
+ fir16_flush(&ec->fir_state);
+ fir16_flush(&ec->fir_state_bg);
+ ec->fir_state.curr_pos = ec->taps - 1;
+ ec->fir_state_bg.curr_pos = ec->taps - 1;
+ for (i = 0; i < 2; i++)
+ memset(ec->fir_taps16[i], 0, ec->taps * sizeof(int16_t));
- ec->curr_pos = ec->taps - 1;
- ec->Pstates = 0;
+ ec->curr_pos = ec->taps - 1;
+ ec->Pstates = 0;
}
+
EXPORT_SYMBOL_GPL(oslec_flush);
-/*- End of function --------------------------------------------------------*/
-void oslec_snapshot(struct oslec_state *ec) {
- memcpy(ec->snapshot, ec->fir_taps16[0], ec->taps*sizeof(int16_t));
+void oslec_snapshot(struct oslec_state *ec)
+{
+ memcpy(ec->snapshot, ec->fir_taps16[0], ec->taps * sizeof(int16_t));
}
+
EXPORT_SYMBOL_GPL(oslec_snapshot);
-/*- End of function --------------------------------------------------------*/
/* Dual Path Echo Canceller ------------------------------------------------*/
int16_t oslec_update(struct oslec_state *ec, int16_t tx, int16_t rx)
{
- int32_t echo_value;
- int clean_bg;
- int tmp, tmp1;
-
- /* Input scaling was found be required to prevent problems when tx
- starts clipping. Another possible way to handle this would be the
- filter coefficent scaling. */
-
- ec->tx = tx; ec->rx = rx;
- tx >>=1;
- rx >>=1;
-
- /*
- Filter DC, 3dB point is 160Hz (I think), note 32 bit precision required
- otherwise values do not track down to 0. Zero at DC, Pole at (1-Beta)
- only real axis. Some chip sets (like Si labs) don't need
- this, but something like a $10 X100P card does. Any DC really slows
- down convergence.
-
- Note: removes some low frequency from the signal, this reduces
- the speech quality when listening to samples through headphones
- but may not be obvious through a telephone handset.
-
- Note that the 3dB frequency in radians is approx Beta, e.g. for
- Beta = 2^(-3) = 0.125, 3dB freq is 0.125 rads = 159Hz.
- */
-
- if (ec->adaption_mode & ECHO_CAN_USE_RX_HPF) {
- tmp = rx << 15;
+ int32_t echo_value;
+ int clean_bg;
+ int tmp, tmp1;
+
+ /* Input scaling was found be required to prevent problems when tx
+ starts clipping. Another possible way to handle this would be the
+ filter coefficent scaling. */
+
+ ec->tx = tx;
+ ec->rx = rx;
+ tx >>= 1;
+ rx >>= 1;
+
+ /*
+ Filter DC, 3dB point is 160Hz (I think), note 32 bit precision required
+ otherwise values do not track down to 0. Zero at DC, Pole at (1-Beta)
+ only real axis. Some chip sets (like Si labs) don't need
+ this, but something like a $10 X100P card does. Any DC really slows
+ down convergence.
+
+ Note: removes some low frequency from the signal, this reduces
+ the speech quality when listening to samples through headphones
+ but may not be obvious through a telephone handset.
+
+ Note that the 3dB frequency in radians is approx Beta, e.g. for
+ Beta = 2^(-3) = 0.125, 3dB freq is 0.125 rads = 159Hz.
+ */
+
+ if (ec->adaption_mode & ECHO_CAN_USE_RX_HPF) {
+ tmp = rx << 15;
#if 1
- /* Make sure the gain of the HPF is 1.0. This can still saturate a little under
- impulse conditions, and it might roll to 32768 and need clipping on sustained peak
- level signals. However, the scale of such clipping is small, and the error due to
- any saturation should not markedly affect the downstream processing. */
- tmp -= (tmp >> 4);
+ /* Make sure the gain of the HPF is 1.0. This can still saturate a little under
+ impulse conditions, and it might roll to 32768 and need clipping on sustained peak
+ level signals. However, the scale of such clipping is small, and the error due to
+ any saturation should not markedly affect the downstream processing. */
+ tmp -= (tmp >> 4);
#endif
- ec->rx_1 += -(ec->rx_1>>DC_LOG2BETA) + tmp - ec->rx_2;
+ ec->rx_1 += -(ec->rx_1 >> DC_LOG2BETA) + tmp - ec->rx_2;
+
+ /* hard limit filter to prevent clipping. Note that at this stage
+ rx should be limited to +/- 16383 due to right shift above */
+ tmp1 = ec->rx_1 >> 15;
+ if (tmp1 > 16383)
+ tmp1 = 16383;
+ if (tmp1 < -16383)
+ tmp1 = -16383;
+ rx = tmp1;
+ ec->rx_2 = tmp;
+ }
- /* hard limit filter to prevent clipping. Note that at this stage
- rx should be limited to +/- 16383 due to right shift above */
- tmp1 = ec->rx_1 >> 15;
- if (tmp1 > 16383) tmp1 = 16383;
- if (tmp1 < -16383) tmp1 = -16383;
- rx = tmp1;
- ec->rx_2 = tmp;
- }
+ /* Block average of power in the filter states. Used for
+ adaption power calculation. */
- /* Block average of power in the filter states. Used for
- adaption power calculation. */
+ {
+ int new, old;
+
+ /* efficient "out with the old and in with the new" algorithm so
+ we don't have to recalculate over the whole block of
+ samples. */
+ new = (int)tx *(int)tx;
+ old = (int)ec->fir_state.history[ec->fir_state.curr_pos] *
+ (int)ec->fir_state.history[ec->fir_state.curr_pos];
+ ec->Pstates +=
+ ((new - old) + (1 << ec->log2taps)) >> ec->log2taps;
+ if (ec->Pstates < 0)
+ ec->Pstates = 0;
+ }
- {
- int new, old;
+ /* Calculate short term average levels using simple single pole IIRs */
- /* efficient "out with the old and in with the new" algorithm so
- we don't have to recalculate over the whole block of
- samples. */
- new = (int)tx * (int)tx;
- old = (int)ec->fir_state.history[ec->fir_state.curr_pos] *
- (int)ec->fir_state.history[ec->fir_state.curr_pos];
- ec->Pstates += ((new - old) + (1<<ec->log2taps)) >> ec->log2taps;
- if (ec->Pstates < 0) ec->Pstates = 0;
- }
-
- /* Calculate short term average levels using simple single pole IIRs */
-
- ec->Ltxacc += abs(tx) - ec->Ltx;
- ec->Ltx = (ec->Ltxacc + (1<<4)) >> 5;
- ec->Lrxacc += abs(rx) - ec->Lrx;
- ec->Lrx = (ec->Lrxacc + (1<<4)) >> 5;
-
- /* Foreground filter ---------------------------------------------------*/
-
- ec->fir_state.coeffs = ec->fir_taps16[0];
- echo_value = fir16(&ec->fir_state, tx);
- ec->clean = rx - echo_value;
- ec->Lcleanacc += abs(ec->clean) - ec->Lclean;
- ec->Lclean = (ec->Lcleanacc + (1<<4)) >> 5;
-
- /* Background filter ---------------------------------------------------*/
-
- echo_value = fir16(&ec->fir_state_bg, tx);
- clean_bg = rx - echo_value;
- ec->Lclean_bgacc += abs(clean_bg) - ec->Lclean_bg;
- ec->Lclean_bg = (ec->Lclean_bgacc + (1<<4)) >> 5;
-
- /* Background Filter adaption -----------------------------------------*/
-
- /* Almost always adap bg filter, just simple DT and energy
- detection to minimise adaption in cases of strong double talk.
- However this is not critical for the dual path algorithm.
- */
- ec->factor = 0;
- ec->shift = 0;
- if ((ec->nonupdate_dwell == 0)) {
- int P, logP, shift;
-
- /* Determine:
-
- f = Beta * clean_bg_rx/P ------ (1)
-
- where P is the total power in the filter states.
-
- The Boffins have shown that if we obey (1) we converge
- quickly and avoid instability.
-
- The correct factor f must be in Q30, as this is the fixed
- point format required by the lms_adapt_bg() function,
- therefore the scaled version of (1) is:
-
- (2^30) * f = (2^30) * Beta * clean_bg_rx/P
- factor = (2^30) * Beta * clean_bg_rx/P ----- (2)
-
- We have chosen Beta = 0.25 by experiment, so:
-
- factor = (2^30) * (2^-2) * clean_bg_rx/P
-
- (30 - 2 - log2(P))
- factor = clean_bg_rx 2 ----- (3)
-
- To avoid a divide we approximate log2(P) as top_bit(P),
- which returns the position of the highest non-zero bit in
- P. This approximation introduces an error as large as a
- factor of 2, but the algorithm seems to handle it OK.
-
- Come to think of it a divide may not be a big deal on a
- modern DSP, so its probably worth checking out the cycles
- for a divide versus a top_bit() implementation.
- */
-
- P = MIN_TX_POWER_FOR_ADAPTION + ec->Pstates;
- logP = top_bit(P) + ec->log2taps;
- shift = 30 - 2 - logP;
- ec->shift = shift;
-
- lms_adapt_bg(ec, clean_bg, shift);
- }
-
- /* very simple DTD to make sure we dont try and adapt with strong
- near end speech */
-
- ec->adapt = 0;
- if ((ec->Lrx > MIN_RX_POWER_FOR_ADAPTION) && (ec->Lrx > ec->Ltx))
- ec->nonupdate_dwell = DTD_HANGOVER;
- if (ec->nonupdate_dwell)
- ec->nonupdate_dwell--;
+ ec->Ltxacc += abs(tx) - ec->Ltx;
+ ec->Ltx = (ec->Ltxacc + (1 << 4)) >> 5;
+ ec->Lrxacc += abs(rx) - ec->Lrx;
+ ec->Lrx = (ec->Lrxacc + (1 << 4)) >> 5;
- /* Transfer logic ------------------------------------------------------*/
+ /* Foreground filter --------------------------------------------------- */
- /* These conditions are from the dual path paper [1], I messed with
- them a bit to improve performance. */
+ ec->fir_state.coeffs = ec->fir_taps16[0];
+ echo_value = fir16(&ec->fir_state, tx);
+ ec->clean = rx - echo_value;
+ ec->Lcleanacc += abs(ec->clean) - ec->Lclean;
+ ec->Lclean = (ec->Lcleanacc + (1 << 4)) >> 5;
- if ((ec->adaption_mode & ECHO_CAN_USE_ADAPTION) &&
- (ec->nonupdate_dwell == 0) &&
- (8*ec->Lclean_bg < 7*ec->Lclean) /* (ec->Lclean_bg < 0.875*ec->Lclean) */ &&
- (8*ec->Lclean_bg < ec->Ltx) /* (ec->Lclean_bg < 0.125*ec->Ltx) */ )
- {
- if (ec->cond_met == 6) {
- /* BG filter has had better results for 6 consecutive samples */
- ec->adapt = 1;
- memcpy(ec->fir_taps16[0], ec->fir_taps16[1], ec->taps*sizeof(int16_t));
- }
- else
- ec->cond_met++;
- }
- else
- ec->cond_met = 0;
+ /* Background filter --------------------------------------------------- */
- /* Non-Linear Processing ---------------------------------------------------*/
+ echo_value = fir16(&ec->fir_state_bg, tx);
+ clean_bg = rx - echo_value;
+ ec->Lclean_bgacc += abs(clean_bg) - ec->Lclean_bg;
+ ec->Lclean_bg = (ec->Lclean_bgacc + (1 << 4)) >> 5;
- ec->clean_nlp = ec->clean;
- if (ec->adaption_mode & ECHO_CAN_USE_NLP)
- {
- /* Non-linear processor - a fancy way to say "zap small signals, to avoid
- residual echo due to (uLaw/ALaw) non-linearity in the channel.". */
+ /* Background Filter adaption ----------------------------------------- */
- if ((16*ec->Lclean < ec->Ltx))
- {
- /* Our e/c has improved echo by at least 24 dB (each factor of 2 is 6dB,
- so 2*2*2*2=16 is the same as 6+6+6+6=24dB) */
- if (ec->adaption_mode & ECHO_CAN_USE_CNG)
- {
- ec->cng_level = ec->Lbgn;
-
- /* Very elementary comfort noise generation. Just random
- numbers rolled off very vaguely Hoth-like. DR: This
- noise doesn't sound quite right to me - I suspect there
- are some overlfow issues in the filtering as it's too
- "crackly". TODO: debug this, maybe just play noise at
- high level or look at spectrum.
- */
-
- ec->cng_rndnum = 1664525U*ec->cng_rndnum + 1013904223U;
- ec->cng_filter = ((ec->cng_rndnum & 0xFFFF) - 32768 + 5*ec->cng_filter) >> 3;
- ec->clean_nlp = (ec->cng_filter*ec->cng_level*8) >> 14;
-
- }
- else if (ec->adaption_mode & ECHO_CAN_USE_CLIP)
- {
- /* This sounds much better than CNG */
- if (ec->clean_nlp > ec->Lbgn)
- ec->clean_nlp = ec->Lbgn;
- if (ec->clean_nlp < -ec->Lbgn)
- ec->clean_nlp = -ec->Lbgn;
+ /* Almost always adap bg filter, just simple DT and energy
+ detection to minimise adaption in cases of strong double talk.
+ However this is not critical for the dual path algorithm.
+ */
+ ec->factor = 0;
+ ec->shift = 0;
+ if ((ec->nonupdate_dwell == 0)) {
+ int P, logP, shift;
+
+ /* Determine:
+
+ f = Beta * clean_bg_rx/P ------ (1)
+
+ where P is the total power in the filter states.
+
+ The Boffins have shown that if we obey (1) we converge
+ quickly and avoid instability.
+
+ The correct factor f must be in Q30, as this is the fixed
+ point format required by the lms_adapt_bg() function,
+ therefore the scaled version of (1) is:
+
+ (2^30) * f = (2^30) * Beta * clean_bg_rx/P
+ factor = (2^30) * Beta * clean_bg_rx/P ----- (2)
+
+ We have chosen Beta = 0.25 by experiment, so:
+
+ factor = (2^30) * (2^-2) * clean_bg_rx/P
+
+ (30 - 2 - log2(P))
+ factor = clean_bg_rx 2 ----- (3)
+
+ To avoid a divide we approximate log2(P) as top_bit(P),
+ which returns the position of the highest non-zero bit in
+ P. This approximation introduces an error as large as a
+ factor of 2, but the algorithm seems to handle it OK.
+
+ Come to think of it a divide may not be a big deal on a
+ modern DSP, so its probably worth checking out the cycles
+ for a divide versus a top_bit() implementation.
+ */
+
+ P = MIN_TX_POWER_FOR_ADAPTION + ec->Pstates;
+ logP = top_bit(P) + ec->log2taps;
+ shift = 30 - 2 - logP;
+ ec->shift = shift;
+
+ lms_adapt_bg(ec, clean_bg, shift);
}
- else
- {
- /* just mute the residual, doesn't sound very good, used mainly
- in G168 tests */
- ec->clean_nlp = 0;
- }
- }
- else {
- /* Background noise estimator. I tried a few algorithms
- here without much luck. This very simple one seems to
- work best, we just average the level using a slow (1 sec
- time const) filter if the current level is less than a
- (experimentally derived) constant. This means we dont
- include high level signals like near end speech. When
- combined with CNG or especially CLIP seems to work OK.
- */
- if (ec->Lclean < 40) {
- ec->Lbgn_acc += abs(ec->clean) - ec->Lbgn;
- ec->Lbgn = (ec->Lbgn_acc + (1<<11)) >> 12;
- }
- }
- }
-
- /* Roll around the taps buffer */
- if (ec->curr_pos <= 0)
- ec->curr_pos = ec->taps;
- ec->curr_pos--;
-
- if (ec->adaption_mode & ECHO_CAN_DISABLE)
- ec->clean_nlp = rx;
-
- /* Output scaled back up again to match input scaling */
-
- return (int16_t) ec->clean_nlp << 1;
+
+ /* very simple DTD to make sure we dont try and adapt with strong
+ near end speech */
+
+ ec->adapt = 0;
+ if ((ec->Lrx > MIN_RX_POWER_FOR_ADAPTION) && (ec->Lrx > ec->Ltx))
+ ec->nonupdate_dwell = DTD_HANGOVER;
+ if (ec->nonupdate_dwell)
+ ec->nonupdate_dwell--;
+
+ /* Transfer logic ------------------------------------------------------ */
+
+ /* These conditions are from the dual path paper [1], I messed with
+ them a bit to improve performance. */
+
+ if ((ec->adaption_mode & ECHO_CAN_USE_ADAPTION) &&
+ (ec->nonupdate_dwell == 0) &&
+ (8 * ec->Lclean_bg <
+ 7 * ec->Lclean) /* (ec->Lclean_bg < 0.875*ec->Lclean) */ &&
+ (8 * ec->Lclean_bg <
+ ec->Ltx) /* (ec->Lclean_bg < 0.125*ec->Ltx) */ ) {
+ if (ec->cond_met == 6) {
+ /* BG filter has had better results for 6 consecutive samples */
+ ec->adapt = 1;
+ memcpy(ec->fir_taps16[0], ec->fir_taps16[1],
+ ec->taps * sizeof(int16_t));
+ } else
+ ec->cond_met++;
+ } else
+ ec->cond_met = 0;
+
+ /* Non-Linear Processing --------------------------------------------------- */
+
+ ec->clean_nlp = ec->clean;
+ if (ec->adaption_mode & ECHO_CAN_USE_NLP) {
+ /* Non-linear processor - a fancy way to say "zap small signals, to avoid
+ residual echo due to (uLaw/ALaw) non-linearity in the channel.". */
+
+ if ((16 * ec->Lclean < ec->Ltx)) {
+ /* Our e/c has improved echo by at least 24 dB (each factor of 2 is 6dB,
+ so 2*2*2*2=16 is the same as 6+6+6+6=24dB) */
+ if (ec->adaption_mode & ECHO_CAN_USE_CNG) {
+ ec->cng_level = ec->Lbgn;
+
+ /* Very elementary comfort noise generation. Just random
+ numbers rolled off very vaguely Hoth-like. DR: This
+ noise doesn't sound quite right to me - I suspect there
+ are some overlfow issues in the filtering as it's too
+ "crackly". TODO: debug this, maybe just play noise at
+ high level or look at spectrum.
+ */
+
+ ec->cng_rndnum =
+ 1664525U * ec->cng_rndnum + 1013904223U;
+ ec->cng_filter =
+ ((ec->cng_rndnum & 0xFFFF) - 32768 +
+ 5 * ec->cng_filter) >> 3;
+ ec->clean_nlp =
+ (ec->cng_filter * ec->cng_level * 8) >> 14;
+
+ } else if (ec->adaption_mode & ECHO_CAN_USE_CLIP) {
+ /* This sounds much better than CNG */
+ if (ec->clean_nlp > ec->Lbgn)
+ ec->clean_nlp = ec->Lbgn;
+ if (ec->clean_nlp < -ec->Lbgn)
+ ec->clean_nlp = -ec->Lbgn;
+ } else {
+ /* just mute the residual, doesn't sound very good, used mainly
+ in G168 tests */
+ ec->clean_nlp = 0;
+ }
+ } else {
+ /* Background noise estimator. I tried a few algorithms
+ here without much luck. This very simple one seems to
+ work best, we just average the level using a slow (1 sec
+ time const) filter if the current level is less than a
+ (experimentally derived) constant. This means we dont
+ include high level signals like near end speech. When
+ combined with CNG or especially CLIP seems to work OK.
+ */
+ if (ec->Lclean < 40) {
+ ec->Lbgn_acc += abs(ec->clean) - ec->Lbgn;
+ ec->Lbgn = (ec->Lbgn_acc + (1 << 11)) >> 12;
+ }
+ }
+ }
+
+ /* Roll around the taps buffer */
+ if (ec->curr_pos <= 0)
+ ec->curr_pos = ec->taps;
+ ec->curr_pos--;
+
+ if (ec->adaption_mode & ECHO_CAN_DISABLE)
+ ec->clean_nlp = rx;
+
+ /* Output scaled back up again to match input scaling */
+
+ return (int16_t) ec->clean_nlp << 1;
}
+
EXPORT_SYMBOL_GPL(oslec_update);
-/*- End of function --------------------------------------------------------*/
/* This function is seperated from the echo canceller is it is usually called
as part of the tx process. See rx HP (DC blocking) filter above, it's
precision, which noise shapes things, giving very clean DC removal.
*/
-int16_t oslec_hpf_tx(struct oslec_state *ec, int16_t tx) {
- int tmp, tmp1;
+int16_t oslec_hpf_tx(struct oslec_state * ec, int16_t tx)
+{
+ int tmp, tmp1;
- if (ec->adaption_mode & ECHO_CAN_USE_TX_HPF) {
- tmp = tx << 15;
+ if (ec->adaption_mode & ECHO_CAN_USE_TX_HPF) {
+ tmp = tx << 15;
#if 1
- /* Make sure the gain of the HPF is 1.0. The first can still saturate a little under
- impulse conditions, and it might roll to 32768 and need clipping on sustained peak
- level signals. However, the scale of such clipping is small, and the error due to
- any saturation should not markedly affect the downstream processing. */
- tmp -= (tmp >> 4);
+ /* Make sure the gain of the HPF is 1.0. The first can still saturate a little under
+ impulse conditions, and it might roll to 32768 and need clipping on sustained peak
+ level signals. However, the scale of such clipping is small, and the error due to
+ any saturation should not markedly affect the downstream processing. */
+ tmp -= (tmp >> 4);
#endif
- ec->tx_1 += -(ec->tx_1>>DC_LOG2BETA) + tmp - ec->tx_2;
- tmp1 = ec->tx_1 >> 15;
- if (tmp1 > 32767) tmp1 = 32767;
- if (tmp1 < -32767) tmp1 = -32767;
- tx = tmp1;
- ec->tx_2 = tmp;
- }
-
- return tx;
+ ec->tx_1 += -(ec->tx_1 >> DC_LOG2BETA) + tmp - ec->tx_2;
+ tmp1 = ec->tx_1 >> 15;
+ if (tmp1 > 32767)
+ tmp1 = 32767;
+ if (tmp1 < -32767)
+ tmp1 = -32767;
+ tx = tmp1;
+ ec->tx_2 = tmp;
+ }
+
+ return tx;
}
+
EXPORT_SYMBOL_GPL(oslec_hpf_tx);
MODULE_LICENSE("GPL");
projects / linux-2.6-omap-h63xx.git / blobdiff