Use a ribbon when you are trying to minimize mic bleed. Use a ribbon on a source with lots of transient spikes since it will smooth them out. Tie a yellow ribbon round the old oak tree.

I tend to grab a ribbon for any instrument that might exhibit harshness in the high end... banjo, hammer dulcimer, mando. The ribbon tends to smooth the harsh transient/percussive nature of these. But also will use very often on fiddle, cittern, bagpipes, etc. The more you use your mics, the more you will learn their unique characteristics.
Be sure to be careful on quiet sources... the ribbons need a lot of gain and you need a really quiet preamp with a lot of gain or you risk introducing audible noise floor into your recording. I use an AEA RPQ preamp for this and can highly recommend it!
I own both a pair of Fatheads and a pair of Royer 121s, plus others. I'm a huge ribbon fan and am happy to see the attention they are gaining of late.

Jeff

Hack, welcome back! Member 1442 ya!
Ribbons simply put, are smooth and take eq very well. I love my Royers.

I only have a Nady ribbon, but I use it on my vocals - I tend to hiss and spit a lot, and it smooths out my voice nicely.

I have been using ribbon microphones for over 30 years. My first ribbon used was the Beyer M 260 & 500. I didn't own those. My first pair were the Beyer M 160's. Followed by a second pair. Followed by a M 130 bidirectional version. With that 130 & the 160, I have a most beautiful MS pair with a pair of flanking M 160's. It's so lush & full on orchestral recording at the Kennedy Center concert Hall. I also landed a pair of RCA 77 DX's. One from the late 1950s in TV gray and the other, the last production run from 1968 with the large block lettered RCA insignia. It looks rather queer without the lightning bolt.

Female vocalists, brass instruments, stringed instruments. You have to realize that these microphones are a.k.a. "Velocity Microphones". While they seem to smooth things out because of their natural high-frequency roll off, they actually captured transients even better than condenser microphones. They prevent overload on things like shakers & tambourines. They are however extremely windy sensitive and not something I would generally utilize on bass drum. If you're new Royer is one of the " heavy duty" varieties, you might want to risk one on some crappy rock 'n roll? But if there isn't a good contract behind the tracking session, it's foolhardy to use it in that capacity. Not necessarily the Cascades as those are affordable. So you can risk their little lives just like Radio Shaft microphones, without regrets. You'll also find that their not quite in phase or out of phase with dynamic and/or condenser microphones. Because of this, they can also be used in different proximity to other microphones without fear of terrible phasing effects. In close-up studio situations, noise generally is not much of a problem. But if you're trying to catch that super quiet oboe solo from over 30 feet away, you'll be hissing like a snake in no time. And I don't think those phantom powered nor tube powered ribbon microphones sound quite as close as their passive sisters. Though sound almost like condenser microphones and that's not always what I want. So I prefer the passive ones.

As a general rule, I don't use my expensive microphones on cheap sessions. You have to weigh the law of probability. That's why I like some of these new Chinese import ribbon microphones. It gives everybody the ability to own one and not have to cry when one gets broken. I'm even considering getting a pair of cheapies to have something to sacrifice for rock 'n roll? I was fairly impressed with the Fat Heads when I first heard them. Sure, they had a bit of a boxy like sound to them that I really didn't care for. But hey, it was just that Chinese transformer. For $100 extra, you can get the optional Cinamag transformer which probably transforms that microphone into something more like my 77's/160/130's, for around $250 US. What a bargain! Buy a bag full! Give them out like business cards and then everybody will know you're serious about ribbon microphones.

Women like ribbons. Ribbons like women.
Mx. Remy Ann David

Ribbons excel on brass instruments.