From ee40a2e7e4867a769765d447a15ac88832eb8aa0 Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Fri, 21 Oct 2022 10:33:41 -0700
Subject: Add an IIR filter option for UHJ encoding/decoding

This uses the reversed-allpass trick to maintain linear phase. with a 256-
sample look-ahead/delay to minimize distortion. This should better preserve low
frequencies while maintaining a proper phase response.
---
 alc/alc.cpp     | 6 ++++--
 alc/panning.cpp | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

(limited to 'alc')

diff --git a/alc/alc.cpp b/alc/alc.cpp
index e89ad598..1f70569a 100644
--- a/alc/alc.cpp
+++ b/alc/alc.cpp
@@ -1148,9 +1148,11 @@ void alc_initconfig(void)
     if(auto uhjfiltopt = ConfigValueStr(nullptr, "uhj", "filter"))
     {
         if(al::strcasecmp(uhjfiltopt->c_str(), "fir256") == 0)
-            UhjQuality = UhjLengthLq;
+            UhjQuality = UhjQualityType::FIR256;
         else if(al::strcasecmp(uhjfiltopt->c_str(), "fir512") == 0)
-            UhjQuality = UhjLengthHq;
+            UhjQuality = UhjQualityType::FIR512;
+        else if(al::strcasecmp(uhjfiltopt->c_str(), "iir") == 0)
+            UhjQuality = UhjQualityType::IIR;
         else
             WARN("Unsupported uhj/filter: %s\n", uhjfiltopt->c_str());
     }
diff --git a/alc/panning.cpp b/alc/panning.cpp
index 6447f0f8..0e6b68d4 100644
--- a/alc/panning.cpp
+++ b/alc/panning.cpp
@@ -1060,7 +1060,7 @@ void aluInitRenderer(ALCdevice *device, int hrtf_id, al::optional<StereoEncoding
 
     if(stereomode.value_or(StereoEncoding::Default) == StereoEncoding::Uhj)
     {
-        if(UhjQuality >= UhjLengthHq)
+        if(UhjQuality != UhjQualityType::FIR256)
             device->mUhjEncoder = std::make_unique<UhjEncoder<UhjLengthHq>>();
         else
             device->mUhjEncoder = std::make_unique<UhjEncoder<UhjLengthLq>>();
-- 
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