Artemus, it certainly is not Voodoo, nor is it in the mind, your digestive system or the mood of your significant other. Highly evolved and heavily tweaked systems are like highly tuned racing engines. Changes in temperature, humidity, fuel (in our case electricity), changes in tire pressure,( balancing out of the front end) will certainly influence performance. Lp performance I've found for example, will be best at about 25 degrees centigrate and at a humidity of not less than 60%. Just my 2 cents.
Cheers,
Cheers,