Stereo to Mono Folddown Mystery

[Tidwells@aol.com]

I've recorded Motu's excellent old MachFive 3 Fazioli Piano VI in a project. When I solo the piano track and then click "mono" folddown on the master track, it sounds softer than if I put a trim plug on the piano track and pan both sides to center. I was just checking for mono compatibility..... With only one speaker on, the piano volume seems to stay the same when I enable and disable the "mono-izing" trim plug, but the volume gets softer than normal when I enable mono fold down on the master track.

To make things even more interesting, If I play the whole mix and put a "mono-izing" trim plug on the master fader channel, the whole mix gets about 2-3 decibels louder, but it stays the same when switching mono fold down on and off. Why would the stereo sample piano VI respond differently than other sounds to the two different "mono-izing" processes? And why is mono folddown different from using a mono-izing trim plug? Please enlighten me, Oh Wise Ones

Doug

[HCMarkus]

I'm guessing DP has a built-in gain reduction when using Master track Fold Down, like DP offers as an option when changing a stereo file to mono in the Soundbites Window.

When the Master Track input is mono, this reduction may be disabled.

Anyone have a definitive answer?

[Killahurts]

Could there be a phase/polarity issue here? Sounds like some of the symptoms you describe.. but if so, where in the chain?

[dix]

The exact same thing happens when folding surround mixes to stereo. It’s been a huge PIA for a long time. I have reported it to support more than once. I think Matt said it was a known issue during one of the webinars, but support didn’t seem to be aware. Using a downmix plugin, such as Nugen Halo, is a workaround, but an expensive one. Adding a +10db (!) Trim to the Master Fader, that I enable whenever I Folddown from 5.1 to stereo is another. Pro Tools does not exhibit this behavior.

[Tidwells@aol.com]

Mysteries solved, I think.... HCMarkus was on the right track: After more experimenting, it seems that a master track fold down from stereo to mono does cause a 3 decibel reduction in signal strength, which sounds right in most cases. After careful investigation, I found that the piano VI which I was monitoring is a couple of decibels stronger in the left channel because it was sampled that way for the range of notes I was playing. I was monitoring only through the left speaker, so when I enabled mono fold down, I was hearing the average of the two stereo signals, which was probably about 1 or 1.5 decibels lower than the left side alone, then with the 3 decibels subtracted for the fold down process. If I monitor only through the right speaker, I don't hear a noticeable volume difference when folding down. And when I have both speakers on, the folded and non-folded volume levels seem to match, which I believe is the purpose of the 3 db reduction they put in the fold down process. I was worried that the piano would sound weak in the mix if the end user is listening through a tiny mono cellphone speaker, but now I'm hoping it will be alright.

Doug

[EMRR]

One follows a pan law, the other doesn’t. Some DAW offer pan law options as there’ve been different standards followed by different hardware console manufacturers.

[dix]

I guess this is a different phenomena than the surround folddown issue. I'd love to get others to report it. MOTU hasn't responded to my TechNotes. A 10db discrepancy between the surround and the stereo folddown is substantial, and really should be addressed.

Here's a video of a 5.1 project with only one stereo track assigned to LR (nothing going to surrounds or LFE) as you can see simply flipping to stereo decreases the output by 10db.

https://youtube.com/shorts/joOd9VgEy_Y