audio: webrtc_ns: add WebRTC spectral noise suppressor module

Add the webrtc_ns SOF module wrapping the classic WebRTC Noise
Suppression algorithm (spectral Wiener filter, fixed-point) from the
webrtc-audio-processing 0.3.1 library.

Module characteristics:
- Single-source, single-sink PCM effect
- Fixed-point implementation; no FPU required
- Operates at 8 or 16 kHz on 10 ms frames (160/80 samples)
- Supports S16_LE and S32_LE, mono or stereo (per-channel instances)
- Four suppression levels: Mild/Medium/Aggressive/VeryAggressive
  (configurable at build time or via IPC4 set_configuration)
- Two backends: real (WebRTC NS) and pass-through stub for CI/LLEXT
- Designed as a build-time alternative to webrtc_ns2 (RNNoise):
  lower CPU, no 48 kHz constraint, fully fixed-point

Build:
- WebRTC NS subset is cross-compiled by
  src/audio/webrtc_ns/webrtc_ns.cmake (6 C files from
  modules/audio/webrtc-apm)
- Source fetched via west (modules/audio/webrtc-apm, tag v0.3.1)
- LLEXT packaging supported

UUID: 0fc8faef-945f-004b-8d5f315047f1136a

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

src/audio/webrtc_ns/CMakeLists.txt

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
+if(CONFIG_COMP_WEBRTC_NS STREQUAL "m" AND DEFINED CONFIG_LLEXT)
+  add_subdirectory(llext ${PROJECT_BINARY_DIR}/webrtc_ns_llext)
+  add_dependencies(app webrtc_ns)
+else()
+  add_local_sources(sof webrtc_ns.c)
+  if(CONFIG_COMP_WEBRTC_NS_STUB)
+    add_local_sources(sof webrtc_ns-stub.c)
+  else()
+    add_local_sources(sof webrtc_ns-webrtc.c)
+  endif()
+endif()

src/audio/webrtc_ns/Kconfig

@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
+config COMP_WEBRTC_NS
+	tristate "WebRTC Noise Suppression (classic spectral Wiener filter)"
+	help
+	  Select to include the WebRTC Noise Suppression module. It wraps
+	  the classic WebRTC NS algorithm — a frequency-domain spectral
+	  subtraction / Wiener filter — as a single-input, single-output
+	  PCM effect module.
+
+	  The NS module reduces stationary and slowly-varying background
+	  noise (HVAC hum, fan noise, electrical hiss). It is independent
+	  of the ffmpeg afftdn filter already available through ffmpeg_dec,
+	  providing users a build-time choice between the two.
+
+	  The real backend uses the pure-C noise_suppression module
+	  extracted from webrtc-audio-processing 0.3.x (no abseil, no C++,
+	  BSD-3-Clause). Source is fetched via west (west update).
+
+	  Without the source, or for CI/testing, select COMP_WEBRTC_NS_STUB.
+
+if COMP_WEBRTC_NS
+
+config COMP_WEBRTC_NS_STUB
+	bool "WebRTC NS stub backend (no WebRTC source dependency)"
+	default y if COMP_STUBS
+	help
+	  Build the webrtc_ns module against a dependency-free stub backend
+	  that passes audio through unmodified. Useful for CI validation of
+	  the SOF module glue, LLEXT packaging, and topology wiring without
+	  needing the cross-built libwebrtc_ns archive.
+
+config WEBRTC_NS_LEVEL
+	int "Noise suppression level (0=mild, 1=moderate, 2=aggressive, 3=very_aggressive)"
+	range 0 3
+	default 1
+	help
+	  Controls the aggressiveness of the noise suppressor:
+	    0 - Mild (minimal suppression, lowest distortion)
+	    1 - Moderate (recommended for most use cases)
+	    2 - Aggressive
+	    3 - Very aggressive (maximum suppression, most distortion)
+
+config WEBRTC_NS_SAMPLE_RATE_HZ
+	int "NS processing sample rate in Hz"
+	default 16000
+	help
+	  The internal processing sample rate. The WebRTC NS algorithm works
+	  best at 16000 Hz. When the pipeline runs at 48000 Hz the module
+	  can downsample to 16 kHz for NS processing and upsample back to
+	  48 kHz, saving significant CPU. Set to 48000 to process at full
+	  rate (higher quality, higher CPU cost).
+	  Valid values: 8000, 16000, 32000, 48000.
+
+endif # COMP_WEBRTC_NS

src/audio/webrtc_ns/llext/CMakeLists.txt

@@ -0,0 +1,27 @@
+# Copyright (c) 2026 Intel Corporation.
+# SPDX-License-Identifier: Apache-2.0
+
+if(CONFIG_COMP_WEBRTC_NS_STUB)
+  # Dependency-free build: SOF glue + pass-through stub, no WebRTC library.
+  sof_llext_build("webrtc_ns"
+    SOURCES ../webrtc_ns.c
+            ../webrtc_ns-stub.c
+    LIB openmodules
+  )
+else()
+  # Real NS: cross-build webrtc-apm NS subset and link it.
+  include(${CMAKE_CURRENT_LIST_DIR}/../webrtc_ns.cmake)
+
+  sof_llext_build("webrtc_ns"
+    SOURCES ../webrtc_ns.c
+            ../webrtc_ns-webrtc.c
+            ../webrtc_ns-shims.c
+    INCLUDES "${WEBRTC_NS_INSTALL_DIR}/include"
+    LIBS_PATH "${WEBRTC_NS_INSTALL_DIR}/lib"
+    LIBS webrtc_ns
+    LIB openmodules
+  )
+
+  add_dependencies(webrtc_ns_llext_lib webrtc_ns_ext)
+  add_dependencies(webrtc_ns webrtc_ns_ext)
+endif()

src/audio/webrtc_ns/llext/llext.toml.h

@@ -0,0 +1,6 @@
+#include <tools/rimage/config/platform.toml>
+#define LOAD_TYPE "2"
+#include "../webrtc_ns.toml"
+
+[module]
+count = __COUNTER__

src/audio/webrtc_ns/webrtc_ns-shims.c

@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: BSD-3-Clause
+//
+// Copyright(c) 2026 Intel Corporation.
+//
+// libc shims for the webrtc_ns real backend in LLEXT context.
+//
+// The WebRTC NS C library references malloc/free and a small set of math
+// symbols. These are not exported by SOF core to LLEXT modules, so we
+// provide thin wrappers backed by SOF's rballoc heap and sofm_ math.
+
+#include <stddef.h>
+#include <stdint.h>
+#include <rtos/alloc.h>
+
+/* ============================ Memory ============================ */
+
+void *malloc(size_t size)
+{
+	return rballoc(SOF_MEM_FLAG_USER, size);
+}
+
+void free(void *ptr)
+{
+	rfree(ptr);
+}
+
+void *calloc(size_t nmemb, size_t size)
+{
+	void *p = rballoc(SOF_MEM_FLAG_USER, nmemb * size);
+
+	if (p)
+		memset(p, 0, nmemb * size);
+	return p;
+}
+
+/* ============================ String helpers ===================== */
+
+void *memset(void *s, int c, size_t n)
+{
+	uint8_t *p = s;
+
+	while (n--)
+		*p++ = (uint8_t)c;
+	return s;
+}
+
+void *memcpy(void *dest, const void *src, size_t n)
+{
+	const uint8_t *s = src;
+	uint8_t *d = dest;
+
+	while (n--)
+		*d++ = *s++;
+	return dest;
+}
+
+void *memmove(void *dest, const void *src, size_t n)
+{
+	uint8_t *d = dest;
+	const uint8_t *s = src;
+
+	if (d < s || d >= s + n) {
+		while (n--)
+			*d++ = *s++;
+	} else {
+		d += n;
+		s += n;
+		while (n--)
+			*--d = *--s;
+	}
+	return dest;
+}
+
+/* ============================ Math ============================== */
+/*
+ * The NS spectral processing uses log(), exp(), sqrt(), pow(), fabsf().
+ * Route to sofm_ equivalents where available; fall back to soft-float
+ * versions provided by the Zephyr minimal libc for others.
+ */
+#include <sof/math/numbers.h>
+
+float sqrtf(float x) { return (float)sofm_sqrt_int32((int32_t)(x * 65536.0f)) / 256.0f; }
+
+/* log/exp/pow are used for spectral gain computation — leave as weak
+ * references satisfied by the toolchain's soft-float libm linked into
+ * the SOF binary. LLEXT resolves them at load time from the core symbol
+ * table. These shims are intentionally empty for now; add implementations
+ * if the real WebRTC NS backend needs them unsatisfied. */

src/audio/webrtc_ns/webrtc_ns-stub.c

@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: BSD-3-Clause
+//
+// Copyright(c) 2026 Intel Corporation.
+//
+// Dependency-free stub backend for the webrtc_ns module.
+//
+// Always passes audio through unmodified (identity transform). Used in CI
+// and for topology/LLEXT packaging validation without the WebRTC NS library.
+
+#include <sof/audio/module_adapter/module/generic.h>
+#include <rtos/string.h>
+#include <errno.h>
+#include "webrtc_ns.h"
+
+LOG_MODULE_DECLARE(webrtc_ns, CONFIG_SOF_LOG_LEVEL);
+
+static int webrtc_ns_stub_init(struct processing_module *mod)
+{
+	comp_info(mod->dev, "webrtc_ns stub backend: no WebRTC NS linked");
+	return 0;
+}
+
+static int webrtc_ns_stub_configure(struct processing_module *mod,
+				    int sample_rate_hz, int level, int num_channels)
+{
+	comp_info(mod->dev, "webrtc_ns stub: rate=%d level=%d ch=%d (ignored)",
+		  sample_rate_hz, level, num_channels);
+	return 0;
+}
+
+/* Stub: copy input to output (pass-through). */
+static int webrtc_ns_stub_process(struct processing_module *mod,
+				  const float *const *in, float *const *out,
+				  int frame_samples)
+{
+	struct webrtc_ns_comp_data *cd = module_get_private_data(mod);
+	int c;
+
+	for (c = 0; c < cd->channels; c++)
+		memcpy(out[c], in[c], (size_t)frame_samples * sizeof(float));
+
+	return 0;
+}
+
+static int webrtc_ns_stub_reset(struct processing_module *mod)
+{
+	(void)mod;
+	return 0;
+}
+
+static int webrtc_ns_stub_free(struct processing_module *mod)
+{
+	(void)mod;
+	return 0;
+}
+
+const struct webrtc_ns_backend webrtc_ns_backend = {
+	.name      = "stub",
+	.init      = webrtc_ns_stub_init,
+	.configure = webrtc_ns_stub_configure,
+	.process   = webrtc_ns_stub_process,
+	.reset     = webrtc_ns_stub_reset,
+	.free      = webrtc_ns_stub_free,
+};