Question: In your blog page titled "Blu-ray Audio Explained," you explain the benefits of Dolby TrueHD and DTS-HD Master Audio on Blu-ray soundtracks. Do Dolby TrueHD and DTS-HD Master Audio improve the sound of standard music CDs? Since there seems to be big improvement in sound using Dolby TrueHD and DTS-HD Master Audio, I would hope to see concert videos become available in Blu-ray format.

Answer: Dolby TrueHD and DTS-HD Master Audio (DTS-MA) are "lossless" compression schemes. By lossless compression, it means the digital information is compressed to save space (like a computer ZIP file), but the sound quality of the original studio master tape is completely retained. "Uncompressed PCM" is another version of lossless sound, but it does not use compression so it takes up much more space on the disc. Content producers have largely moved to Dolby TrueHD and DTS-MA so they can use the saved space on better video quality or more special features.

There are no Dolby TrueHD or DTS-MA tracks found on CD discs, so CD playback will not benefit from having the feature on your electronics. A Blu-ray audio-only format is under development, and there are indeed many concerts available for purchase on Blu-ray. One of my favorites is "The Pyongyang Concert," featuring the January 2008 performance of the New York Philharmonic in Pyongyang, North Korea. It contains the full concert with lossless PCM soundtracks in both stereo and 5.1 surround, as well as an excellent documentary recounting their visit. Video and sound quality is top-notch, and the second encore, the Korean folk song "Arirang," is both beautiful and haunting. If you are a fan of classical concerts, documentaries or international politics, be sure to check it out.

When Blu-ray was launched, usage of the two formats was split about evenly between the studios, but as of late DTS-MA has taken a commanding lead. I have received e-mails from readers touting the sonic superiority of DTS-MA over Dolby TrueHD, or uncompressed PCM over either; but the truth is they are all sonically identical when recorded the same way from the same master tape.

Any sonic differences are due to the master tape used or tweaking done by the technicians. As long as you have one of the lossless formats and the equipment to decode it, you are assured of the finest possible sound quality.

Qusetion: What is meant by a "prime" lens? I have been reading about digital SLRs on message boards and frequently see this term.

Answer: A prime lens is a lens that does not vary its focal length, such as a 50 mm or 100 mm. Zoom lenses are lenses that vary their focal length, such as 14-42 mm or 50-200 mm. If you divide the larger number by the smaller number, you get the zoom range. A 14-42 mm is a 3x zoom, a 50-200 mm is a 4x zoom.

Many photographers prefer prime lenses because they tend to be sharper than zooms, and they work better in low light. If you have a Canon digital SLR, you really should have its excellent 50 mm 1.8 lens in your bag. It is only $100, and the difference in sharpness compared to the kit zoom will shock you. Pentax has excellent prime lenses (the pancake series) as well.

First Published: September 18, 2009, 11:30 p.m.