My studio gear is currently set up inside my garage, and lately it has been freezing cold inside. Though there is no surface moisture on the gear (so I am assuming that nothing is condensing), I am worried that my gear could be affected by sub‑zero temperatures overnight.
Via SOS web site
SOS Technical Editor Hugh Robjohns replies: If you look at the specifications for any piece of electronic equipment (normally printed in the handbook or available on‑line), you will usually see a specification for the acceptable storage and operating temperature ranges (and sometimes a figure for acceptable humidity too). The range of temperatures in which a product can be stored is usually significantly wider than that in which it can be operated, and both are generally wider than the range of temperatures typically experienced in the UK.
So the short answer is that for most people it is unlikely that their equipment will suffer damage overnight just because of cold temperatures. Be aware, however, that a lot of plastics do become significantly stiffer or more brittle in the cold, so cables will be less flexible and plastic components are more likely to break. This is more likely to be an issue with tape and video recorders, or other machines with moving parts, than with computers and mixers, but worth bearing in mind all the same.
Humidity is usually a more serious problem, though, and you are right to be more concerned about that. Condensation forms when warm, humid air comes into contact with something much colder, taking that air below the dew point. I wouldn't expect to see condensation on the equipment in the morning because both air and equipment will be at the same temperature. The problem will come when the air in the room starts to heat up (because of the heat from your body, the room lighting and any equipment you switch on), but the equipment remains cold (initially, at least). The condensation that forms can cause all manner of electrical problems, ranging from potentially very serious electrical short-circuits at one extreme to annoying intermittent computer glitches at the other, and mechanical problems such as rust and corrosion.
The best approach is to keep the room comfortably above the dew point by having some form of safe low‑level background heating overnight. A night storage heater or an oil‑filled electric radiator is probably the best solution — and it's always more pleasant and inspiring to walk into a studio that has some residual warmth than trying to become motivated in a freezing‑cold room!