When I decided to do MP3s as backing tracks for my duo (for the same reason as Craig - file size) I tested it this way.
I set up my PA set, consisting of two EV-ZLX15P speakers and a Samson 12 channel analog mixer.
I removed all FX and EQ to keep that from influencing the sound
I hooked my synth modules up to two channels so that the sound was live--not recorded
I recorded WAV and various resolution MP3 files and hooked them up to two channels in the same mixer
The MP3 files were ripped with CDex with the LAME encoder, and with the Quality setting at the highest (Q=0)
I adjusted the volumes so both the synth rack and recorded files were at 75db, "A" weighted, SLOW response.
Next I sat 4 musicians down. One just had her hearing tested and was found as perfect as can be, another worked in a store that sold high-end sound equipment, and the others I trusted to have good ears.
The musicians sat with their backs to me, so they couldn't see what I was doing. I played the audio and various recordings, and they wrote down their impressions.
Nobody could not tell the difference between the synth rack, the WAV files and the 224kbps MP3 files. I'm sure there was a degradation in both the WAV and the 224kbps MP3 files, and I'm sure lab equipment could measure it. However, trained ears on a high-end PA system could not tell the difference.
At 192 kbps all but one listener could hear the very slightest difference in the highest frequencies. I could hear it too. I doubt that anyone without trained ears listening in a quiet room could notice it, it was that slight. Not only that, but I swapped channels at this point between the synth rack and MP3 files to make sure the mixer channels weren't the difference. They weren't.
At 128 kbps we could all hear the difference. Probably adequate for causal listening in a noisy environment like a car, but not good enough for stage. The high frequency loss was more noticeable, the dynamic response seemed reduced and the general clarity and separation of the instruments was degraded. Anything under 128 was pure trash.
Since no room I play in is either a perfect listening environment, certainly not quiet, and hopefully full of an audience that is having a great time eating, drinking, listening, and dancing to the music, I figured 192kbps was optimum for my needs.
BTW, I make my own backing tracks, playing all the parts myself in real time into a MIDI sequencer; Generally an orphaned Master Tracks Pro. It's a straight sequencer with great editing tools and no audio to get in the way, so everything is available from one click of the menu bar (no sub menus and sub-sub-menus). This allows me to spend more time on the MIDI controllers (synth keyboard, wind controller, drum controller, etc.) and less time on the computer keyboard. The synths and sound modules consist of Yamaha TX81z, Yamaha VL70m, Korg i3, Korg DS8, Roland MT32, Roland XV5050, Roland SC55, Edirol SD90, Ketron SD2 and both a Peavey and Akai hardware samplers that I sampled my own bass, drum, and other instrument samples. I choose what I consider the sound for each part from whatever synth I think sounds best in that song.
In other words, we're listening to high quality sounds on a high-end PA set.
Of course this is my personal experience, and depending on your ears, the app and encoder you are ripping your files with, the system you are playing them through, and a few other things, your experience might be quite different.
Insights and incites by Notes
