HDC (Hybrid Digital Coding or High-Definition Coding) with SBR (spectral band replication) is a proprietary lossy audio compression codec developed by iBiquity for use with HD Radio. It replaced the earlier PAC codec in 2003.[1][2] In June 2017, the format was reverse engineered and determined to be a variant of HE-AACv1.[3] It uses a modified discrete cosine transform (MDCT) audio coding data compression algorithm.[4]