Noises related to combustion are an important characteristic of any gas or diesel engine driven vehicle. The presence or lack of it can contribute to a vehicle being perceived as powerful or weak, reliable or problematic. Combustion noise can be appreciated, even patented. But it can also be an unwanted addition to the soundscape. A type of combustion related noise, termed growl, can be one of those unwanted additions. The noise is similar to diesel clatter and has been described as making an engine sound “like a piece of farm equipment.”
Being a detriment to a vehicle’s sound quality, it is vital to determine a way in objective plots to show the degree a vehicle may exhibit growl. An experienced NVH analyst may be able to uncover it in the standard frequency spectrum, but it may be difficult to establish when discussing with less experienced colleagues.
A method using Modulation Analysis has been developed that displays when growl is audible and can be used to compare levels of growl in vehicle recordings. The purpose of this paper is to share the analysis techniques and provide a foundation to build on when isolating growl noise in objective data.