I used to buy digitrax decoders to match the command station down at the club (brand loyalty I guess), but now my goal is to have sound in everything that I plan to run so I stopped buying basic decoders. The only basic decoder installations would be in engines that I will never get a sound decoder for because they are electric locomotives, or because they are too old for my modelling era, but would be kept in a corner to run for show sometimes (like my GG1)
Soundtraxx Tsunami wins hand down for all EMD sounds. Quantum Revolution wins with their digitally manipulated GE sounds. The Tsunami GE sound decoder is great, but the problem is that the sounds from the decoder are genuine sounds that cannot physically be reproduced with a speaker that fits in an HO scale engine.
Example:
What it sounds like in an HO Scale loco:
http://www.youtube.com/watch?v=HGSxcyNtkvQ
Not so good huh?
What it sounsd like if connected to loudspeakers and subwoofer:
http://www.youtube.com/watch?v=lDwUuw67_lM
Amazing
QSI has gotten around the laws of physics by digitally manipulating the prime mover sounds on the GE prime movers so that it tricks our ears and brains to make us beleive that we are hearing the really low toned chugs.
QSI sound decoders in the Atlas Gold Series are NOT a good example to compare QSI to Soundtraxx. The Atlas Gold engines feature an older model of the QSI decoder and not the Quantum Revolution. The Quantum Revolution has user-editable sound files that can be changed with the Quantum Programmer. The older QSI decoders do not support this feature without a chip upgrade.
The Atlas Gold EMD 645 prime mover doesn't sound right because all you hear is the turbocharger whine and nothing else. It sounds more like a squeal than a whine. The 567s aren't really correct either.
Although the GE FDL prime mover sounds pretty good on the older QSI models, it's not quite correct either.
Quantum Revolution solves all of those problems.