We get calls like this all the time. An upstairs neighbor stomps around, moves furniture and vacuums in the middle of the night. The conga (or trumpet, or piano) player next door practices for an hour a day, but each day at a different time. A water pump makes a loud hum at random intervals. The restaurant downstairs plays loud music, but only when there's a party. The opera teacher upstairs sings whenever the spirit moves her. And of course, a family with "active" children just moved in upstairs.
You can't "teleport" an acoustic consultant or DEP inspector into your apartment to catch such short-lived noises when they happen. And even if you could, you would only have documented one occurrence. This is very important. Residents and even businesses are given a certain amount of leeway for noise that happens only very rarely. In one case we know of, co-op residents lost their case against a restaurant because the consultant they hired (not Acoustilog) made their only measurements on New Year's Eve. One party, even a loud one, does not demonstrate a "pattern of nuisance".
Your noise problem may indeed be a recurring one, but unless you can present convincing evidence to demonstrate that, your opponents can claim that you have "cherry picked" one unusually bad incident.
News: Appellate Court issues injunction in favor of our clients, based on evidence obtained using the Acoustilog Long-Term Recording System
We have assembled a tamper-proof calibrated recording system for situations like this. The studio-quality digital audio recorder records sound from one or more calibrated microphones and vibration sensors. Depending on the number of channels, the system can record for up to 125 hours. Our clients can engage the "Record": function whenever they hear the noise of interest. In fact, the system will actually record sound starting 30 seconds before the "Record" button is pressed, allowing the user to "catch" even very short-lived sounds. The system can even discriminate against noises coming from other sources.
The system is calibrated on site. This allows us to play back the audio in court at the same level that it was heard in the client's home. This provides very convincing evidence. The judge doesn't have to imagine what "100Hz at 64 dB" sounds like; we can demonstrate it. The date and exact time of each occurrence is also documented on the recording, allowing time-correlated graphs of the noise disturbance to be made.