Why does Apollo sound so good?
The sound quality has always been an important factor when making decisions in the decoder code. Recent addition of 32-bit and 24-bit output has resulted in further improvements in the quality. To prove this, I measured the difference of Apollo 37zm 24-bit output to the MPEG-1 audio layer 3 compliance test reference signal (ISO/IEC 11172-4). More info on the test and results for a bunch of other players (including an old version of Apollo) can be found here. The results for Apollo 37zm 24-bit output are RMS level 7.169×10−10 and maximum difference 1.192×10−7. For comparison, the same values for the latest MAD decoder (MPEG Audio Decoder 0.15.1b) built with accuracy optimizations enabled and 24-bit output without dithering are RMS level 8.804×10−8 and maximum difference 4.768×10−7. The difference is quite obvious and favorable to Apollo: RMS level is over a hundred times the one produced by Apollo 37zm and the maximum difference is four times the one by Apollo (interestingly the results
