  Phase processing has been replaced by group delay processing for the
extraction of source and system parameters from speech. Group delay functions
are ill-behaved when the transfer function has zeros that are close to unit
circle in the z-domain. The modified group delay function addresses this
problem and has been successfully used for formant and monopitch estimation. In
this paper, modified group delay functions are used for multipitch estimation
in concurrent speech. The power spectrum of the speech is first flattened in
order to annihilate the system characteristics, while retaining the source
characteristics. Group delay analysis on this flattened spectrum picks the
predominant pitch in the first pass and a comb filter is used to filter out the
estimated pitch along with its harmonics. The residual spectrum is again
analyzed for the next candidate pitch estimate in the second pass. The final
pitch trajectories of the constituent speech utterances are formed using pitch
grouping and post processing techniques. The performance of the proposed
algorithm was evaluated on standard datasets using two metrics; pitch accuracy
and standard deviation of fine pitch error. Our results show that the proposed
algorithm is a promising pitch detection method in multipitch environment for
real speech recordings.
