Convention Paper
A Highly Optimized Nonlinear Least Squares Technique for Sinusoidal Analysis: From (Omega)(K2N) to (Omega)(N log (N))
AES Convention 116 · Paper 6045 · May 2004
Abstract
In the field of sinusoidal modelling, two types of least
squares amplitude estimation methods are distinguished. A first
group of methods estimate the complex amplitude of each sinusoid
in an iterative manner. Although their main disadvantage is that
they are unable to resolve overlapping frequency responses, they
are used frequently because of their computational complexity
being O(N log (N)). By contrast, methods that compute
all amplitudes simultaneously can resolve overlapping frequency
responses but their computational complexity scales with a power
of three in function of the number of sinusoidal components. In
this work a method is proposed which allows to compute all
amplitudes simultaneously and still has an O(N log (N)) complexity. This is realized by explicitly including a
window with a bandlimited frequency response in the least squares
derivation resulting in a band diagonal system of equations which
can be solved in linear time. Since overlapping frequency
responses are allowed, an iterative method must be used to
optimize the frequencies resulting in a nonlinear least squares
technique. A commonly used technique is Newton optimization which
requires the computation of the gradient and the Hessian matrix.
Also here, the same computational gain is realized by applying the
same methodology.
