Optical frequency combs (OFCs) have led to numerous achievements in metrology, with multi-heterodyne spectroscopy being an outstanding example [1-3]. Recently, we have demonstrated a robust “acousto-optic” frequency comb (AO-OFC), based on a frequency-shifting loop (FSL), which features hundreds or even more than 1000 mutually coherent lines [4]. We have proven the capability of this comb modality to perform self-heterodyne and multi-heterodyne (i.e. “dual-comb”) spectroscopy [4]. Here, we provide a model for the intuitive understanding of the performance of the AO-OFC in the steady state configuration, taking into account the key system parameters such as amplified spontaneous emission (ASE) and the gain saturation. This model explains the experimental features of AO-OFCs, and can be used to optimize the parameters of AO-OFCs. © 2019 IEEE