Fix UHJ encoding/decoding factors

Classic B-Format uses scaling factors W=1, X=sqrt(2), Y=sqrt(2), and Z=sqrt(2),
which is +3dB louder than FuMa. The base factors are designed assuming classic
scaling, so encoding a 0dBFS FuMa signal without accounting for this would
result in the UHJ signal peaking at about -3dBFS. Similarly, decoding UHJ to
FuMa B-Format would be +3dB louder than intended.

So encoding needs to implicitly boost the signal by +3dB, and decoding needs to
attenuate by -3dB.

1 files changed, 3 insertions, 1 deletions

diff --git a/utils/uhjdecoder.cpp b/utils/uhjdecoder.cpp
index f9db4895..cda16a40 100644
--- a/utils/uhjdecoder.cpp
+++ b/utils/uhjdecoder.cpp
@@ -492,8 +492,10 @@ int main(int argc, char **argv)
                 decoder->decode2(inmem.get(), decmem, got);
             for(size_t i{0};i < got;++i)
             {
+                /* Attenuate by -3dB for FuMa output levels. */
+                constexpr float sqrt1_2{0.707106781187f};
                 for(size_t j{0};j < outchans;++j)
-                    outmem[i*outchans + j] = f32AsLEBytes(decmem[j][i]);
+                    outmem[i*outchans + j] = f32AsLEBytes(decmem[j][i] * sqrt1_2);
             }
 
             size_t wrote{fwrite(outmem.get(), sizeof(byte4)*outchans, got, outfile.get())};