From b120a7c39762aeb5afb06b06f8972ebb53facf43 Mon Sep 17 00:00:00 2001
From: George Norton <george_norton_uk@hotmail.com>
Date: Sat, 26 Aug 2023 16:59:37 +0100
Subject: [PATCH] Fix off by one error in fix_28_t

---
 firmware/code/fix16.inl | 9 +++++----
 firmware/code/run.c     | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/firmware/code/fix16.inl b/firmware/code/fix16.inl
index ca45a2e..bca6f14 100644
--- a/firmware/code/fix16.inl
+++ b/firmware/code/fix16.inl
@@ -32,11 +32,12 @@ static inline fix3_28_t norm_fix3_28_from_s16sample(int16_t a) {
     /* So, we're using a Q3.28 fixed point system here, and we want the incoming
        audio signal to be represented as a number between -1 and 1. To do this,
        we need the 16-bit value to map to the 28-bit right-of-decimal field in
-       our fixed point number. 28-16 = 12, so we shift the incoming value by
+       our fixed point number. The 16 bit samples are siged, so bit 15 needs to
+       be positioned at bit 28. 28-15 = 13, so we shift the incoming value by
        that much to covert it to the desired Q3.28 format and do the normalization
        all in one go.
     */
-    return (fix3_28_t)a << 12;
+    return (fix3_28_t)a << 13;
 }
 
 /// @brief Convert fixed point samples into signed integer. Used to convert
@@ -69,9 +70,9 @@ static inline int16_t norm_fix3_28_to_s16sample(fix3_28_t a) {
         }
     }
     /* When we converted the USB audio sample to a fixed point number, we applied
-       a normalization, or a gain of 1/65536. To convert it back, we can undo that
+       a normalization, or a gain of 1/32767. To convert it back, we can undo that
        by shifting it back by the same amount we shifted it in the first place. */
-    return (a >> 12);
+    return (a >> 13);
 }
 
 static inline fix3_28_t fix3_28_from_flt(float a) {
diff --git a/firmware/code/run.c b/firmware/code/run.c
index 3a33f89..50711c1 100644
--- a/firmware/code/run.c
+++ b/firmware/code/run.c
@@ -194,7 +194,7 @@ void __no_inline_not_in_flash_func(core1_entry)() {
                 x_f16 = bqf_transform(x_f16, &bqf_filters_right[j],
                     &bqf_filters_mem_right[j]);
 
-                out[i] = (int16_t) norm_fix3_28_to_s16sample(x_f16);
+                out[i] = (int32_t) norm_fix3_28_to_s16sample(x_f16);
             }
         }