What is High-Resolution Audio? - Part 2

by John Siau April 03, 2014 3 min read

What is High-Resolution Audio? - Part 2

By John Siau

April 4, 2014

High-Resolution Audio systems offer the promise of an extended high-frequency range. High-Resolution digital systems now operate at 2 to 4 times the sample rate of the standard CD. This means that these systems have the capability of extending the playback frequency range well above the 22 kHz limit of the standard CD. Does this added high-frequency range improve our listening experience? How high is high enough? Do we really need anything over 20 kHz?

In the previous post I stated that "High-Resolution Audio will only truly arrive when the sum total of all defects in the audio chain become inaudible". In that post I discussed the need for low noise components. In this post I will look at frequency response. How much bandwidth do we need to satisfy the 20 Hz to 20 kHz limitation of the best human ears? Is a 20 kHz bandwidth good enough for High-Resolution Audio? If not, why not?

Let's assume we have a playback system consisting of a CD player, a preamplifier, a power amplifier and speakers. If each of these has a 20 Hz to 20 kHz frequency response, is this sufficient to reproduce all of the frequencies we can hear? The short answer is no. Here is why:

The frequency response of a system can be determined by summing the frequency response of each component in the audio chain. If two components are - 3 dB at 20 kHz, then together they are - 6 dB at 20 kHz. If we look at our example system, we have four components in the chain: CD player, preamplifier, power amplifier, and speakers. If all are -3 dB at 20 kHz, then we have a system response that is -12 dB at 20 kHz. Worse yet, this system will typically measure -4 dB at 10 kHz. This system will not come close to meeting the performance of our ears! Each individual component was well matched to the limitation of our ears, but as a system, these components cannot achieve anything resembling High-Resolution Audio.

If we want to accurately reproduce 20 kHz audio, the frequency response of each component must extend well beyond 20 kHz. For this reason, Benchmark products are engineered to achieve a 200 kHz to 500 kHz bandwidth. Is this excessive and unnecessary? To answer this, let's replace each of the four components in our sample system with components that have a 200 kHz bandwidth. The combined system now measures - 4 dB at 100 kHz, - 0.8 dB at 50 kHz, and about - 0.2 dB at 20 kHz. This simple 4-component signal chain achieves a 100 kHz bandwidth and is well-matched to the 96 kHz bandwidth of a 192 kHz digital sample rate.  We could legitimately argue that the region between 20 kHz and 100 kHz may offer little musical content, and even if it does, we may not be able to detect its presence. The real benefit is that we have preserved the entire 20 Hz to 20 kHz bandwidth after passing through four audio components in a typical playback system.

Professional audio systems often have very long analog signal chains. These applications place difficult demands on the frequency response of each analog component in the chain. A chain of 16 analog components, each with a bandwidth of 20 kHz, will produce an overall response of about - 3 dB at 5 kHz. This is telephone quality at best! If the same system is built with 200 kHz components, the overall response will be - 3 dB at 50 kHz, and about -1 dB at 20 kHz. Benchmark's founder, Allen H. Burdick, identified this problem when investigating the poor performance of analog audio distribution within television facilities in the mid 1980's. Performance of these analog systems was improved significantly by increasing the bandwidth of the analog distribution amplifiers. More details on this subject can be found in chapter 3 of  "A Clean Audio Installation Guide" by Allen H. Burdick. Modern video systems use digital audio distribution and are not subject to these cumulative effects.

In summary, very high bandwidth is required at each link in the audio chain if we want to assemble a High-Resolution system. Audio components and digital formats that just meet the requirements of the human ear may be entirely inadequate when connected together in a chain. The audio chain is nowhere near as strong as the weakest link! 



Also in Audio Application Notes

System Performance Calculations
System Performance Calculations

by John Siau March 02, 2023 13 min read

If an audio system is composed of multiple components, we may have detailed specifications for each component, but we will not know the performance of the combined system without doing some calculations. You may have questions such as these:

  • Will my audio system produce audible noise?
  • Will my audio system produce audible distortion?
  • How will my audio components work together as a system?
  • How loud will my audio system play?

Use Benchmark's online audio calculators to find answers!

For example, if we know the output power of an amplifier, as well as the sensitivity and impedance of our loudspeakers, we can calculate the maximum sound pressure level that our system can produce.

PEAK SPL CALCULATOR
Speaker Sensitivity: dB SPL (2.83 V, 1 M)
Amplifier Power Per Channel into 8 Ohms: Watts
RESULTS
Peak Output Level (at typical listening position): dB SPL

 

This application note provides interactive examples that help to answer the questions listed above.

Read More
Audio Calculators
Audio Calculators

by John Siau November 29, 2022 1 min read

We have added an "Audio Calculators" section to our webpage. Click "Calculators" on the top menu to see more like these:

 

THD % to dB Converter
% THD
RESULTS
dB THD
THD dB to % Converter
dB THD
RESULTS
% THD
Read More
SECRETS Q&A WITH JOHN SIAU OF BENCHMARK MEDIA SYSTEMS
SECRETS Q&A WITH JOHN SIAU OF BENCHMARK MEDIA SYSTEMS

by Benchmark Media Systems January 07, 2022 1 min read

Secrets contributor Sumit Chawla recently caught up with Benchmark’s VP and Chief Designer, John Siau to get a little more in-depth on several subjects.

John Siau, VP Engineering, Benchmark Media Systems, Inc.

Q: "Benchmark is one of the few companies that publishes an extensive set of measurements, but you also balance that with subjective testing. Can you talk about the equipment, the listening room, and the process for subjective testing?"

Q: "Was there ever a time where you learned something from a subjective test that was not captured by measurements?"

Q: "You conducted some listening tests to determine whether distortion in the “First Watt” was audible. What test material did you use for this, and what did you find?"

Q: "The AHB2 amplifier incorporates THX Audio Achromatic Amplifier technology. When and how did the partnership with THX come about?"

Q: "Linear power supplies have been and remain quite popular in high-end devices. You favor switch-mode power supplies. When and why did you make this switch?"

... and more!

Read the full interview here 

Read More