The "official" noise criteria that a new motor vehicle has to conform to (Transport Canada), use a drive-by test procedure that is exceptionally difficult to replicate in "actual field conditions" by the roadside. Remember that the slightest deviation from procedure will result in the test result being thrown out in court. The "official" noise test is viable for an original vehicle manufacturer to do, but it's essentially unenforceable at the roadside.
SAE J2825 was designed from the outset to be a simple roadside test, but even that one appears to have aspects of unenforceability due to not having a viable way to measure engine RPM that can't be called into question in court. (A frequency analyzer used on a very well balanced inline four cylinder engine could read twice crank revs, for example.)
SAE J2825 was designed from the outset to be a simple roadside test, but even that one appears to have aspects of unenforceability due to not having a viable way to measure engine RPM that can't be called into question in court. (A frequency analyzer used on a very well balanced inline four cylinder engine could read twice crank revs, for example.)