HQCD

HQCD (HiQuality CD, 高品质 CD) is an audio CD manufacturing standard introduced by Japan’s Memory-Tech. It primarily modifies the disc substrate and reflective layer materials to improve the optical readability of pressed discs. The logical format of HQCD remains CD-DA, storing 44.1 kHz, 16-bit stereo PCM. It can be read by standard CD players and does not include any additional audio layers that require specialized equipment for decoding.

Standard pressed CDs replicate the microscopic pits on a glass master using polycarbonate, which is then coated with a metallic reflective layer. HQCD uses polycarbonate with higher light transmittance and replaces the common aluminum reflective layer with an alloy that has higher reflectivity. It is designed to provide the reading laser with a more stable reflected signal and reduce the impact of manufacturing materials on the pit reading margin; it does not alter the digital content represented by the pits, nor does it expand the 16-bit data to a higher bit depth. Digital discs feature error-correction mechanisms, but this does not mean that the optical signals from all readable discs are identical. Factors such as substrate transparency, pit replication accuracy, the reflective layer, and eccentricity can affect the RF readout waveform; the player then derives PCM data through tracking, clock recovery, and error correction. In computer-based ripping, where the same data can be accurately recovered, an HQCD and a standard CD using the same digital master will produce identical files; if the sound quality of two commercial releases differs, it is necessary to determine whether different master tapes or mastering data were used.

HQCD is a brand of manufacturing materials, not a master processing method. Distributors can produce HQCDs using new remastered masters or use existing CD masters for HQCD pressing; therefore, the disc label alone cannot indicate the recording source, dynamic range, or frequency response. It also differs from HDCD and MQA-CD, which alter the encoding to maintain PCM compatibility, as well as XRCD and K2HD, which emphasize controlled production processes.

UHQCD is another manufacturing solution developed under the same compatibility principles, using a photopolymer replication layer and a different molding process. Both HQCD and UHQCD can be played on standard CD players, but due to differences in materials, replication methods, and product labeling, UHQCD cannot simply be regarded as an upgrade to HQCD in terms of storage capacity or audio bit depth.