I have a project (just solo piano with nice Cathedral verb with long trails). I found that when mixing down the project to MP3 It seems that my reverb sound much less is than when it's being played back in Reaper. My project sample rate is at 48000 and I'm rendering my MP3 at 48000 using CBR of 320 kbps. Also dithering down at 24bit using 4X oversample. Over all the sound I'm getting is great, but I seem to have to really drive the verb. I figure this was due to the dithering process (data being loss) but just thought I'd ask. Any tips? Thanks

No need to dither and reducing bitdepth when rendering to MP3.

I have sometimes felt the same issue. "felt" means, that I haven't done any research deeper into that. I figured, that somehow "joint stereo" did something the the reverb, whereas with normal "stereo" in the MP3 everything was OK. So I would try experimenting with these parameters. Maybe it solves the problem. Other than that: no, I never overcompensate anything when rendering to MP3. I dont do rendering to MP3, always mix down normally to 24bit/44.1kHz and do conversions outside of Reaper with another program. Never had any problems. Another thing is to use MP3 in VBR -0. I cant recall exactly, but it was something with left out resolution that can be used in other frames to get at certain points a resolution of up to 540kb/sec. Resolution with VBR -0 can be borrowed from places, where resolution isnt needed that much. Something in that line. Of course "joint stereo" or "stereo" should be tried both to get the best result.

MP3 encoder doesn't need dithered input. REAPER feeds it with 32bit floating point (that's why dithering checkboxes are greyed out in REAPER for MP3 rendering). MP3 encoder does the rest. Dithering is required for <32bit WAV formats.

AFAIK, If the source/target bit rates are the same (WAV to WAV), there is no dithering to be done because no bits are truncated.

The default MP3 algorithm gives slight preference to mid instead of side signals, so anything wide won't sound as wide when rendered to MP3, especially at low mid frequencies. Perceptual coding isn't perfect. Reverbs are often somewhat of a wide signal, so maybe that's part of the problem. If it bothers you alot, render to FLAC (lossless) instead. Otherwise you will just have to live with the fact that MP3 is lossy and degrades the audio a bit.

Here's the 24bit and the MP3 to download

I also wanted to say THANKS to everyone for your tremendous help! I have always told all my mates that the Reaper forum is the BEST!