What is High-Resolution Audio? - Part 1
There is a raging debate over the definition of "High-Resolution Audio". The focus of this debate has been misdirected by a lot of marketing hype. High-Resolution Audio will only truly arrive when the sum total of all defects in the audio chain become inaudible. We are not there yet, but we are getting close. The final chapter will not be higher sample rates and more bits. The final chapter will be achieving the necessary improvements to critical components in the signal chain.
Ignore the sample rate and format wars. There are several competing digital systems that are fully capable of delivering true High-Resolution Audio. These include all 24-bit (and higher) PCM systems with sample rates higher than the 44.1 kHz rate used in standard CD's. Double speed DSD is a 1-bit format that is also capable of delivering High-Resolution Audio. Avoid falling for the marketing spin that tells you: "if 96 kHz is great, 192 kHz is better", or "if 24-bits is great, 32-bits must be better". Don't fall for the spin!
As a delivery format, 24-bit digital systems are far better than any other part of the signal chain. Converters, preamplifiers, power amplifiers, and speakers cannot deliver the 144 dB signal to noise ratio (SNR) that can be transmitted through a 24-bit system. Our ears have a limitation of about 130 dB (the difference between the threshold of hearing and the threshold of pain). Our ears are essentially limited to the equivalent of 21 or 22 bits (6 dB per bit if you care to do the math). This means that 24-bit systems have a nice margin beyond our auditory system. It also means that the 96 dB available from a 16-bit CD system is somewhat deficient.
The CD was designed to closely approach the limits of human hearing. The format has almost enough bandwidth, and almost enough dynamic range to be transparent. In contrast, High-Resolution digital formats have more than enough resolution to convey every detail that can be heard by the best human ears. Nevertheless, few people are experiencing the promises of the "High-Resolution" or "High-Definition" marketeers.
Why is High-Resolution Audio failing to deliver? Do we need more bits and more samples? The answer is NO! Don't fall for the spin!
What we need are audio components that are capable of delivering High-Resolution Audio. For example, the D/A converter (DAC) built into the typical DVD player usually has a "24-bit" DAC that only delivers a 90 to 95 dB SNR. This is the equivalent of 15 to 16 bits (CD performance at best). In contrast, the Benchmark DAC2 outboard DAC has an SNR of 126 dB (equivalent to 21 bits). The DAC2 is actually capable of delivering peaks that are 3.5 dB higher, giving the DAC2 a total SNR of 129.5 dB (21.5 bits), matching the limits of human hearing. The DAC2 connects directly to the power amplifier (eliminating a separate "preamplifer" from the signal chain).
But, an outboard DAC is only a partial solution to the High-Resolution Audio dilemma. A second key part of the problem is the performance of the audio power amplifier. A 24-bit audio system is useless if it passes through the typical power amplifier. It is nearly impossible to find power amplifiers that can deliver an SNR higher than about 102 dB. This is the equivalent of 17 bits (adequate for CD applications, but definitely not adequate for High-Resolution Audio). Anyone who thinks they can hear the difference between 16-bit and 24-bit digital audio through a "17-bit" power amplifier is fooling themselves.
Clearly, a system playing High-Resolution Audio through a great outboard DAC, may fail to deliver high-resolution unless the amplifier has adequate performance. For this reason, Benchmark has undertaken the difficult task of building a power amplifier that is worthy of the title "High-Resolution". The new Benchmark AHB2 power amplifier has a 130 dB SNR. Like the DAC2, the AHB2 is well matched to the limits of human hearing. Together, these two devices form a signal chain that can truly deliver High-Resolution Audio to the terminals on the back of a pair of speakers.
In summary, we need to focus on the performance of our playback equipment instead of participating in the High-Resolution format wars. If your playback system can't resolve anything better than CD quality, then "High-Resolution Audio" will remain an illusion.
Also in Audio Application Notes
Interpolator Overload Distortion
Most digital playback devices include digital interpolators. These interpolators increase the sample rate of the incoming audio to improve the performance of the playback system. Interpolators are essential in oversampled sigma-delta D/A converters, and in sample rate converters. In general, interpolators have vastly improved the performance of audio D/A converters by eliminating the need for analog brick wall filters. Nevertheless, digital interpolators have brick wall digital filters that can produce unique distortion signatures when they are overloaded.
10% Distortion
An interpolator that performs wonderfully when tested with standard test tones, may overload severely when playing the inter-sample musical peaks that are captured on a typical CD. In our tests, we observed THD+N levels exceeding 10% while interpolator overloads were occurring. The highest levels were produced by devices that included ASRC sample rate converters.
Audiophile Snake Oil
The Audiophile Wild West
Audiophiles live in the wild west. $495 will buy an "audiophile fuse" to replace the $1 generic fuse that came in your audio amplifier. $10,000 will buy a set of "audiophile speaker cables" to replace the $20 wires you purchased at the local hardware store. We are told that these $10,000 cables can be improved if we add a set of $300 "cable elevators" to dampen vibrations. You didn't even know that you needed elevators! And let's not forget to budget at least $200 for each of the "isolation platforms" we will need under our electronic components. Furthermore, it seems that any so-called "audiophile power cord" that costs less than $100, does not belong in a high-end system. And, if cost is no object, there are premium versions of each that can be purchased by the most discerning customers. A top-of-the line power cord could run $5000. One magazine claims that "the majority of listeners were able to hear the difference between a $5 power cable and a $5,000 power cord". Can you hear the difference? If not, are you really an audiophile?
Making Sound with Plasma - Hill Plasmatronics Tweeter
At the 2023 AXPONA show in Chicago, I had the opportunity to see and hear the Hill Plasmatronics tweeter. I also had the great pleasure of meeting Dr. Alan Hill, the physicist who invented this unique device.
The plasma driver has no moving parts and no diaphragm. Sound is emitted directly from the thermal expansion and contraction of an electrically sustained plasma. The plasma is generated within a stream of helium gas. In the demonstration, there was a large helium tank on the floor with a sufficient supply for several hours of listening.
While a tank of helium, tubing, high voltage power supplies, and the smell of smoke may not be appropriate for every living room, this was absolutely the best thing I experienced at the show!
- John Siau