The main aim of this work was to characterize the perceptual effects introduced by low bit rate spatial audio codecs. The existing methodologies used to assess the performance of spatial audio codecs were reviewed and it was found that spatial audio coding systems have been evaluated using one perceptual attribute – basic audio quality (BAQ). This approach, although effective in terms of the assessment of the overall performance of codecs, does not quantify the contribution of typical codec distortions to the perceived BAQ of the codecs or allow for the identification of independent perceptual attributes that describe the artefacts introduced by spatial audio coding systems. A series of experiments was carried out aiming to characterize the perceptual effects introduced by low bit rate spatial audio codecs. It was found that impairments related to timbral features of the sound are the ones that affect the most the perceived basic audio quality of the codecs. Furthermore, four independent perceptual attributes were uncovered providing a description of the perceptual effects introduced by low bit rate spatial audio codecs.