This still results in some loss of fidelity and audio quality as compared to the studio master, primarily to achieve higher bandwidth reductions for audio information encoded in these formats. As with Dolby Digital and DTS, both DD+ and DTS-HD High Resolution (covered in the next section) use lossy but more efficient compression algorithms to encode data. DD+ is also a constant bitrate (CBR) encoding, which means it operates at the same bitrate at all times, regardless of the compressed audio material it is handling at any given moment. According to Dolby Labs, DD+ achieves compression ratios of around 4:1 (3.75:1, according to some sources). See Table 1 for more information about sound schemes, SPDIF, and HDMI handling for DD+. Those HD DVDs that supported DD+ invariably used 1.5 Mbps bitrates. Audio Bit Rate values can go as high as 6.144 Mbps for encoded data (this translates into 13.5 Mbps uncompressed), but might be either 1.5, 4.5, or 6.144 Mbps, depending on the bandwidth the studio decides to allocate to this type of audio track.Audio Fidelity data: the DD+ specification indicates it can be either 16 or 24 bits deep, and can be recorded at 44.1 kHz, 48 kHz (typical for DVDs and Blu-ray discs), or 96 kHz.
In fact, the only movies we could find that indicated support for DD+ were recorded for HD DVD, such as A View From Space With Heavenly Music, Unleashed, and so forth. Only a very few Blu-ray movies claim to include DD+ encodings, and PowerSquid includes no listings in this category.