HDTV is possible because of the special displays or video monitors recently developed that allow the high resolution electronic digital video signals to be displayed as intended. The high definition viewing experience is flawed without the accompanying sound having a similar degree of resolution. There are no objectively comparable sound monitoring devices for High Definition Audio (HDA).
Audiophiles and the supporting high-end industry have typically sought solutions for the monitoring of high resolution audio however their efforts produce results which are highly subjective, difficult to replicate and have no consideration for cost or size. The HDSS® standard must accomplish what the high-end industry is attempting to achieve but for the mass market application in simple objective monitors which replicate HDA on a sonic level. In essence, the sound must be reproduced objectively as the picture for all situations. In the simplest applications the human voice should be naturally intelligible. The official name for HDSS® certified speakers is that of HDSS® Audio Monitor. Size is a consideration for effective general application of HDSS® audio monitors when they must be externally added to an existing product. Small size also considers all of the necessary elements for full HDSS® certification. Larger HDSS® qualified products will typically deviate from the standard by nature of design. Embedded speaker products can qualify for HDSS® certification but typically not 100% as they are fixed in position.
HDA is available for transmission, recording and playback but at the point of audible playback the high resolution of the electronic signals is obscured by loudspeaker distortions. The preservation of the original audio signal is enhanced due to high sampling rate digital technology while no attempt is made to improve loudspeaker resolution. Currently extremely high resolution digital files such as SACD and DVD audio have no monitoring standard to assure that their detail will be heard. All digital audio files, even lossy, are enhanced with higher resolution at the loudspeaker. At present HDA is only resolved objectively using high quality headphones which is not the goal of sound content producers.
HDA/HDTV must be monitored using high resolution audio monitors. The digital audio portion of the HDTV signal must use a suitable audio transducer that allows for presentation of detail. This objective must be met for normal acoustic conditions without regard to placement as will be the situation with the video monitor. The visual objective for panel TV is to show no external speakers while maintaining High Definition Sound apparently originating from the screen itself. The audio for HDTV must be observable at the close distances available for viewing the screen itself or other positions within the viewing area while maintaining intelligibility and a natural character. Headphones are rarely used to monitor television audio resulting in no currently available standard for HDA/HDTV sound monitoring devices.
1. SINGLE DRIVER - The audio signal for each channel can only be reproduced by one transducer. The audio signal immediately loses its resolution when it is split and reproduced from more than one driver in the frequency range above 100 Hz. A single driver also allows for the micro dimensions required for multi-applications of the HDSS® Audio Monitor.
The ear cannot interpret the detail due to the many negative issues resulting from signal splitting:
2. PISTONIC OPERATION - The single transducer representing the sound monitor for the HDA signals must operate as a piston over the entire audio range to include frequencies from 80 Hz to 20 kHz with little phase error. The angular response must be reasonably flat to 10 kHz and to at least 45 degrees off axis at vertical and horizontal angles. The ability to respond to low frequencies below 80 Hz is essential for operation without a subwoofer even though the output will be with gradual loss. The subwoofer must be an option for HDSS® qualified audio monitors.
The ear cannot interpret detail due to many negative issues related to non-pistonic operation of the single speaker driver.
3. NON RESONANT BASS EXTENSION - The support of extended lower frequencies can only be accomplished using non-resonant devices. HDSS® low frequency extension cannot be accomplished without adequate control of the resonant characteristics of the driver(s) involved. Poor bass extension should be avoided to maintain required detail. The ear cannot interpret detail due to many negative issues related to poorly resolved lower bass frequencies.
The first two requirements listed above must be met with a minimum of negative issues for HDSS® certification. Sound is analogous so maximum detail is resolved when all three conditions above are met. Each negative issue carries weight relative to its degree of influence. A fully resolved HDSS® system will have a degree of resolution unparallel to none with a score of 100%. Each negative issue described above will lower that score. To qualify as an entry level HDSS® monitor the product score must be at least 50%. Anything lower will not be able to officially bear the HDSS® logo. The major specifics of HDSS® require that:
A) The audio monitor be of wide dynamic range with the ability to respond to very low level signals with a great degree of linearity. Maximum level is relative to application.
B) The audio monitor maintain that range at all vertical and horizontal angles within the room so as to include room reflections at the ear. Intelligibility must not suffer.
C) The audio range must be high pass limited to include sub 100 Hz signals while having a moderate slope below that low cutoff frequency. Subwoofer is optional for HDSS®
TBI is currently establishing the weighting values while ongoing research defines the relative effect of some less offensive negative issues required in various applications.