Broadcasters Experience IBOC Listening Tests
Sep 5, 2001 12:00 PM, By Chriss Scherer, editor
New Orleans - Sep 4, 2001 - Attendees at the NAB Radio Show this week have the opportunity to experience the iBiquity IBOC DAB listening tests that were conducted in evaluation of iBiquity's iDAB system.
In two-hour sessions, up to six attendees were given the chance to hear audio samples of various types of music and speech that represent varying levels of audio quality. Some samples were created in an audio lab while others were recorded from actual iBiquity field tests at participating stations.
The test session has three parts. The first part is an introduction and training, where the group is introduced to the PC test interface and given examples of some of the various types of aural effects that will be experienced. The test subjects then go to individual listening rooms for the second and third parts.
Part two is a screening test, which evaluates the test taker's listening ability. Subjects are presented with an original source audio file, and then listen to two samples to determine which sounds most like the original. One of the samples is the original source. The other has an aural artifact in it, which could be multipath, adjacent-channel interference, noise, or a variation in the stereo field.
While test takers of the original test given by Dyna-stat in Dallas used the second part to eliminate unsuitable test takers, the NAB Radio tests allow each subject to complete the entire process so as to better illustrate the system.
The third part of the test is a mean option scoring (MOS) test. Subjects listen to a single audio sample and rate it as Excellent, Good, Fair, Poor, or Bad.. Subjects listen to a total of 178 samples. Subjects can take a break during the process to avoid listening fatigue.
The test setup uses a PC with the stored sound files. Audio is played over a Lynx One sound card and the AES-3 signal is converted to analog with a Lucid Technologies DA9624. For the Individual listening portion, subjects used a pair of Sennheiser HD 600 headphones. For the training period, a single Lucid DA9624 fed a Rane HC 6 headphone amp and listeners used Sony MDR 7509 headphones.
The official listening tests were completed with open speakers, but because of the close confines of the listening room, headphones were substituted for the demonstration.
Following the test period, subjects were able to view and hear a demonstration of the iDAB system and compare analog and digital signals in various field recordings of the IBOC signal.