[Mp4-tech] Poor H.264 PSNR Results with JM73

[Michael Igarta]

Hello,
I am performing some test encodes of mobile CIF (300 frames) using 
latest the JM 7.3 reference software.
The resulting PSNR settings and visual quality seem much worse than I 
should be getting:
I/P Frame QP=30, B Frame QP = 32: PSNR(Y) = 30.79 dB
I/P Frame QP=38, B Frame QP = 40: PSNR(Y) = 25.15 dB
I/P Frame QP=46, B Frame QP = 48: PSNR(Y) = 20.22 dB
Using AHM20 with rate control gives me much better numbers.  Can someone 
tell me what I am doing wrong with the
constant QP?  I changed the following in the default encoder.cfg:
InputFile = "mobile.cif"
LastFrameNumber = 299
FramesToBeEncoded = 299
SourceWidth = 352
SourceHeight = 288
Thanks you very much for any advice.