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The following article presents a new real time implementation of an iterative cepstrum based spectral envelope estimation technique that was originally published under the name true envelope. Because the original algorithm is hardly known outside Japan we will first describe the algorithm and compare it to the standard techniques, i.e. LPC and discrete cepstrum. The estimation properties are compared and it is shown that the true envelope estimator achieves convincing envelope estimations even for problematic, high pitch signals. The algorithm is analyzed with the objective to find an efficient implementation that sufficiently reduces the computational complexity such that the algorithm can be used in real time within the phase vocoder. The implementation that is presented reduces the run time required by the algorithm depending on the cepstral order on the estimation parameters by a factor of $2$ to $9$ such that real time processing becomes feasible.