From 4a26477965ceb9ac3c8c5afda02b5cb68bbb9348 Mon Sep 17 00:00:00 2001
From: Archit Tamarapu <archit.tamarapu@iis.fraunhofer.de>
Date: Wed, 3 Sep 2025 13:03:49 +0200
Subject: [PATCH] allow python fallback for arbitrary low-pass filter cutoff
 frequencies if ITU filter does not support them

---
 .../audiotools/audioarray.py                   |  4 +---
 .../audiotools/convert/__init__.py             | 18 +++++++++++++-----
 .../audiotools/wrappers/filter.py              |  4 ++--
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/ivas_processing_scripts/audiotools/audioarray.py b/ivas_processing_scripts/audiotools/audioarray.py
index 3e7d4c13..62c30d19 100755
--- a/ivas_processing_scripts/audiotools/audioarray.py
+++ b/ivas_processing_scripts/audiotools/audioarray.py
@@ -522,9 +522,7 @@ def lpfilter(
         N, Wn = sig.cheb2ord(fc / (fs / 2), (fc + 500) / (fs / 2), 3, 60)
         b, a = sig.cheby2(N, 60, Wn, "low")
 
-        # Apply the Butterworth filter for each channels, across time axis
-        # y = sig.lfilter(b, a, axis=0) # non zero-phase filter
-        y = sig.filtfilt(b, a, x, axis=0)  # zero-phase filer, batch processing
+        y = sig.filtfilt(b, a, x, axis=0)  # zero-phase filter, batch processing
     else:
         y = x
 
diff --git a/ivas_processing_scripts/audiotools/convert/__init__.py b/ivas_processing_scripts/audiotools/convert/__init__.py
index d7d612af..953742d3 100755
--- a/ivas_processing_scripts/audiotools/convert/__init__.py
+++ b/ivas_processing_scripts/audiotools/convert/__init__.py
@@ -35,9 +35,11 @@ from copy import copy
 from pathlib import Path, PurePath
 from shutil import copyfile
 from typing import Optional, Union
+from warnings import warn
 
 from ivas_processing_scripts.audiotools import audio, audioarray, metadata
 from ivas_processing_scripts.audiotools.audiofile import write
+from ivas_processing_scripts.audiotools.audioarray import lpfilter
 from ivas_processing_scripts.audiotools.convert.channelbased import convert_channelbased
 from ivas_processing_scripts.audiotools.convert.masa import convert_masa
 from ivas_processing_scripts.audiotools.convert.objectbased import convert_objectbased
@@ -335,11 +337,17 @@ def process_audio(
 
     """low-pass filtering"""
     if fc is not None:
-        if logger:
-            logger.debug(
-                f"Applying low-pass filter with cutoff {fc} Hz using ITU STL filter"
-            )
-        x.audio = lpfilter_itu(x, fc)
+        try:
+            if logger:
+                logger.debug(
+                    f"Applying low-pass filter with cutoff {fc}Hz using ITU STL filter"
+                )
+            x.audio = lpfilter_itu(x, fc)
+        except NotImplementedError:
+            warn(f"Low-pass filter cutoff {fc}Hz not supported by ITU filter. Falling back to python implementation.")
+            if logger:
+                logger.debug(f" Applying low-pass filter with cutoff {fc}Hz using python")
+            x.audio = lpfilter(x.audio, fc, x.fs)
 
     """MNRU"""
     if mnru_q is not None:
diff --git a/ivas_processing_scripts/audiotools/wrappers/filter.py b/ivas_processing_scripts/audiotools/wrappers/filter.py
index 3f6ce956..5d79fc00 100755
--- a/ivas_processing_scripts/audiotools/wrappers/filter.py
+++ b/ivas_processing_scripts/audiotools/wrappers/filter.py
@@ -231,8 +231,8 @@ def lpfilter_itu(
     flt_vals = [1500, 3500, 7000, 10000, 12000, 14000, 20000]
     try:
         flt_type = flt_types[flt_vals.index(fc)]
-    except Exception:
-        raise ValueError(f"LP cut-off frequency {fc}Hz not supported.")
+    except ValueError as e:
+        raise NotImplementedError(f"LP cut-off frequency {fc}Hz not supported by ITU filter.") from e
 
     # resample if samplingrate is not supported
     old_fs = None
-- 
GitLab