I am reading a paper, and it is said "state observationprobability densities were single mixture Gaussian observation densities". My question is: Isn't a single mixture gaussian the same that a regular 1-D gaussian?
Single mixture gaussian does not seem to be an accepted term, but it is probably equivalent to a regular gaussian distribution, either univariate or multivariate (more context is needed to tell which).
Without knowing which paper you are talking about, I would guess that the authors modeled state observation distribution as a single gaussian, but wanted to hint that the model could be generalized to a gaussian mixture with $n > 1$ components, even though they did not do so.
edit: paper is here
After reading the context in the paper, I am more confident that the authors intended single mixture gaussian to just mean a normal gaussian distribution, as they talk about a single mean and covariance matrix.