As part of my series of blog posts and slideshows regarding topics of common confusion in home theater, below I cover THX certification, DLNA network access, and distortion and THD. This series features excerpts from my new Kindle book Home Theater for the Internet Age.
- Part 1: Volume in a zero dB world, updating firmware, and the disadvantages of Blu-ray
- Part 2: Speaker resistance and analog vs. digital amps in AV receivers
- Part 3: PCM vs. bitstream and Blu-ray player upscaling/upconversion
- Part 5: HDMI (including cable length and controversial expensive cables)
- Part 6: Closed-back vs. open-back around-ear headphones
- Part 7: Understanding your room and room dynamics
- Part 8: Room correction, speaker position, and more room dynamics
- Part 9: Ethernet, component separates, and broadband internet routers
THX is a collection of audio and video certifications for both commercial cinema (movie theaters) and home theater environments. THX was born at Lucasfilm Studios in the early 1980s, when George Lucas was producing Return of the Jedi, and gained its name from Lucas’ first feature film, THX 1138. Lucas was concerned that the fidelity and overall experience he was creating in his studio wasn’t being translated into commercial cinemas. The first THX certifications were granted to movie theaters, not home theater components.
THX offers several different types of certifications, including those for amplifiers and display panels. To obtain THX certification, a particular component model must pass 200 tests. While THX certification doesn’t guarantee you’ll like the image produced by a display or the sound flowing out of an amplifier, it does ensure a solid performance level. Buying THX-certified equipment helps you get reliable mid to top-tier components with respect to quality and performance. It has little to do with price, however. Products at several different costs may feature the THX logo. It is, however, more common on higher-end, more expensive components.
THX has also released an app for Apple and Android devices that helps calibrate your home theater’s video and audio. For more information regarding home theater calibration, see the Room Calibration section below and the Room Dynamics & Positioning section of the Speakers chapter.
DLNA Local Network Access
DLNA, or the Digital Living Network Alliance, is a communications protocol that works over both wi-fi and Ethernet that allows a variety of media files, such as family photos, music files (including high-resolution varieties), and videos to be streamed from one device to another on a local area network (or LAN). In home theater, DLNA is typically implemented in audio/video receivers and Blu-ray players and accesses a storage device or computer elsewhere on your local network.
Not only must your receiver or Blu-ray player support DLNA, but the device on your network—on which the media files are stored and from which you want to access them—must also include this protocol. This “sending” device on your network could be a personal computer (running Windows 7/8 or Mac OS X), a network storage device (officially called a NAS, or Network Access Storage), or even a top-shelf router with an attached flash drive or USB hard drive. As long as the two devices have a valid connection, enough bandwidth, and DLNA, you can begin routing photos, music, and video from your home network to your receiver or Blu-ray player, using your big display panel and listening to audio and music through your living room speakers.
However, simply because you can use DLNA to get a particular media file from a PC or storage device on your network to your audio/video receiver or Blu-ray player doesn’t mean the receiving device can necessarily decode it. For example, if you have a bunch of high-resolution music files in AIFF format stored on your network, but your receiver (or Blu-ray player) isn’t capable of decoding the AIFF format, DLNA won’t help. DLNA includes no decoding logic or special software for this purpose. It is merely a way for two devices on a home network to recognize each other and stream media files from one to the other.
Distortion & THD
All home theater components produce a certain amount of distortion, something that damages the quality of the sound but, at low and even moderate levels, typically can’t be perceived. This distortion is measured as THD, or Total Harmonic Distortion. In the case of an amplifier, THD is a measurement of the comparison of the receiver’s input and output signals (revealing how much the unit’s amp distorted the audio signal).
Instead of burying you in percentages and decimals, simply realize that lower THD is better. Any reputable brand of AV receiver, Blu-ray player, or speaker, however, will typically exhibit so little THD that it isn’t noticed (except at maybe the loudest volumes). This is true of models at all costs. According to Gary Altunian at Stereos.about.com, “In reality, total harmonic distortion is hardly perceptible to the human ear. Every component adds some level of distortion, but most distortion is insignificant and small differences in specifications between components mean nothing.”
Note that THD becomes worse as volume increases. Most THD ratings for receivers are based on the unit’s full output, or greatest volume (0 db, as you’ll learn below). As a rule of thumb, simply ensure that a receiver’s THD rating is below 1% (typical THD ratings on good receivers are far lower, falling between 0.03% and 0.08%, but measuring techniques vary and are sometimes heavily influenced by a component manufacturer’s marketing department). THD is just one measure of the quality of an amplifier or speaker. If you’re shopping for reputable receiver models, THD shouldn’t typically be an issue that influences your purchasing decision.
Curt Robbins is author of the following books from Amazon Kindle:
- Home Theater for the Internet Age ($9.95)
- Understanding Personal Data Security ($4.99)
- Understanding Home Theater ($4.99)
- Understanding Cutting the Cord ($4.99)
- Understanding Digital Music ($4.99)