In the beginning there was all-analog
In the middle there was an unhappy marriage
In the end there was all-digital
If you look at the history of both audio and video, audio just now entering stage three. Video entered stage three about 15 years ago. With the video transition virtually complete, consumers enjoy high resolution, noise and artifact free, crystal clear, involving picture quality. Display prices and weight have dropped and quality is quite high for both flat panels and front projection technologies.
Analog audio reached its peak before the introduction of the first transistor circa 1960. Since then it’s been a very rough transition period for music lovers. In fact for several decades analog audio still had better sound quality than digital, in spite of the Phillips claim in 1983 that CD format was “perfect sound forever”. Digital finally began to show its merits in the 1990s and begin to supersede analog playback.
However many sonic anomalies remained in spite of the refinements in both digital and analog processing. Early digital was bright and constricted. Manufactures responded with a warmer but less resolving sound quality. Between these extremes, niches were created for “high-end” cables, a dubious solution made popular for several decades.
Today the most common technique is to convert digital audio streams to analog for processing and then several stages of amplification. The problem is low-level analog signal are easily corruptible by higher levels of digital interference.
The obvious solution is to not convert the digital signal to analog. This implies the use of an all-digital processing chain and power amplifier.
However the traditional audio mindset that heavier, bigger and more expensive is always better.
Analog Class D Amplifiers
The most common type is the European based ICE analog class D analog amplifier, which found acceptance in subwoofer amplifiers and then more recently in a few expensive receivers.
Because of the technology available at the (~1990) time, the digital signal was converted to analog. This allowed the delicate mico-volt analog signal to easily become contaminated when input to noisy pulse-width-modulated Class D power amplifier. This also assumes that traditional D/A converters are transparent. Trust me they are not.
These pulsed receivers with traditional D/A converters are at a distinct disadvantage regardless of cost. The analog signal is corrupted during analog conversion and then at every stage thereafter. Then it is amplified 30db! Is this madness or what. Pioneer claims it took their designers two years to make respectable.
Digital Class D Amplifiers
In 2011 the venerable analog conversion is finally avoided, with all-digital amplifiers containing built-in pcm-to-pwm converters and all-digital feedback The best example is the eight channels, 120 watt, HDMI 1.4 Samsung 700 receiver using Pulsus Korean technology. The great efficiency and reduced part count lowers the weight and price, beside offers superior sonics. What more could a consumer ask for?http://www.pulsus.co.kr/english/products/pro_02_05.html
Texas Instruments has also developed an all-digital two channel reference design which features low distortion:http://www.ti.com/ww/en/analog/tas5630/index.shtml
These advances in sonic fidelity and realism are possible since any possible extraneous contamination only occurs after the typical 30db of amplification, in the final output stage.
With minimal legacy analog processing, the receivers back panel real-estate can be drastically reduced. In fact receivers could be 1/4 the current size with no loss in performance. In these all-digital amplifiers, the volume control can change the amplifier gain without distortion.
The benefits of all-digital receivers when combined with other new breakthrough technologies such as speakers incorporating high-gauss neodymium magnets are both compelling and already in place. Companies such as Bose and Apple are already making a fortune. The bigger, heavier, more expensive enthusiast believer will be last to make the change.
A Word of Caution
Class D amplifiers are inherently noisy. It takes expensive gear to measure and properly suppress the interference. However by keeping the signal in digital format until the final amplifier output stage, the high frequency noise is easily filtered out.
Two obstacles preventing progress are identified: consumers who have made large investments in traditional gear and the industry including manufactures and advertiser supported reviewers
I’ve been following this simple rule with excellent success in three systems: avoid mixing analog and digital processing. It’s like mixing oil and water. Don’t do it, as you will never be satisfied with the long-term sound quality, as the interference is everywhere.