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Audio Application Notes

Audio Myth -

Audio Myth - "Damping Factor Isn't Much of a Factor"

by John Siau June 04, 2020

Myth - "Damping Factor Isn't Much of a Factor"

Myth - "A Damping Factor of 10 is High Enough"

Myth - "All Amplifiers Have a High-Enough Damping Factor"

Where did these Myths Originate?

These myths seem to trace back to a well-know paper written by Dick Pierce. His analysis shows that  a damping factor of 10 is virtually indistinguishable from a damping factor of 10,000 when it comes to damping the motion of a loudspeaker cone. This analysis has been examined and repeated in many more recent articles, such as a well-written post on Audiofrog.com by Andy Wehmeyer. Articles such as these are often cited as evidence that amplifier damping factor doesn't matter. The mathematical analyses are correct, but the conclusions are incomplete and misleading!

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COVID-19 ... Don't just survive!

COVID-19 ... Don't just survive!

by John Siau March 23, 2020

A Week Ago, Life was Normal

How fast things can change!

It is March 23, 2020 and we are currently battling the worldwide COVID-19 pandemic.

This application note will be a departure from normal. I will make a few observations about the current situation and then look at the nuts and bolts of how we reconstructed our operations in less than 48 hours. Benchmark is 100% operational, but nothing looks the same as it did last week.

- John Siau

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Rules of Thumb for Music and Audio

Rules of Thumb for Music and Audio

by John Siau April 01, 2019

As an engineer I like to use "rules of thumb" to make quick estimates that help to explain the physical world around me.

These rules of thumb are easy-to-remember approximations that eliminate the need for complicated and needlessly precise calculations.

If you feel discombobulated by the complexities of high school physics, there is hope! I encourage you to step back and take a fresh approach.

If you learn a few simple rules of thumb, you can unravel mysteries of the physical world, amaze your friends, and yourself.

In this paper I will present 15 simple rules that I find useful when working with music and audio.

- John Siau

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Feed-Forward Error Correction

Feed-Forward Error Correction

by John Siau October 11, 2018

The Benchmark AHB2 power amplifier and HPA4 headphone amplifier both feature feed-forward error correction. This correction system is an important subset of the patented THX-AAA™ (Achromatic Audio Amplifier) technology. It is one of the systems that keeps these Benchmark amplifiers virtually distortion free when driving heavy loads. It is also the reason that these amplifiers can support 500 kHz bandwidths without risk of instability when driving reactive loads.

This paper explains the differences between feedback and feed-forward systems. As you read this paper, you will discover that you already understand the benefits of feed-forward correction because you use it instinctively to improve a feedback system commonly found in your automobile. If feed-forward correction can improve your driving experience, it may also improve your listening experience!

- John Siau

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Balanced vs. Unbalanced Analog Interfaces

Balanced vs. Unbalanced Analog Interfaces

by John Siau April 23, 2018

If you look at the back of any Benchmark product, you will find balanced XLR analog-audio connectors. As a convenience, we also provide unbalanced RCA connectors on many of our products. In all cases, the balanced interfaces will provide better performance.

We build our unbalanced interfaces to the same high standards as our balanced interfaces, but the laws of physics dictate that the balanced interfaces will provide better noise performance.

This application note explains the advantages of balanced interfaces.

- John Siau

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Relay-Controlled Volume - The Ultimate Solution for Analog Audio

Relay-Controlled Volume - The Ultimate Solution for Analog Audio

by John Siau April 11, 2018

Benchmark has introduced a new analog-to-analog volume control circuit that features a 256-step relay-controlled attenuator and a 16-step relay-controlled boost amplifier. The volume control has a +15 dB to -122 dB range in 0.5 dB steps and is a key component in the HPA4 Headphone / Line Amplifier.

Our goal was to produce an analog-to-analog volume control with the highest achievable transparency. We wanted to be able to place this volume control in front of our AHB2 power amplifier or in front of our THX-888 headphone amplifier board without diminishing the performance of either device. Our volume control would need to have lower distortion and lower noise than either of these amplifiers. Given the extraordinary performance of these THX-AAA amplifiers, this would not be an easy task!

This application note discusses the engineering decisions that went into the development of this new analog volume control circuit. The end result is a fully buffered volume control with a signal-to-noise ratio that exceeds 135 dB. THD measures better than the -125 dB (0.00006%) limits of our test equipment.

- John Siau

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Laboratory Use of the Benchmark AHB2 Power Amplifier

Laboratory Use of the Benchmark AHB2 Power Amplifier

by John Siau January 26, 2018

SEAS, a well-known manufacturer of high-quality loudspeakers, selected the Benchmark AHB2 as a key component for use in testing loudspeakers. They created an innovative test system that measures loudspeaker motor strength and moving mass with higher accuracy than previous methods. This new measurement system was documented in the December 2017 Journal of the Audio Engineering Society.

According to the AES paper, the SEAS team selected the Benchmark AHB2 for the following reasons:

"A Benchmark AHB2 amplifier is used, which has excellent signal-to-noise ratio and bandwidth, low output impedance, and is suitable for laboratory use (with advanced overload protection)."

The AHB2 was designed to outperform all competing power amplifiers in terms of noise and distortion. The result is an amplifier with unrivaled transparency.

Our goal was to create the ultimate amplifier for the enjoyment of music. It is nice to know that the AHB2 is also being used to test new and improved loudspeakers!

- John Siau

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Interpreting THD Measurements - Think dB not Percent!

Interpreting THD Measurements - Think dB not Percent!

by John Siau November 15, 2017

Distortion measurements (THD, THD+N and IMD) are traditionally expressed in terms of percent. But what do 1%, 0.1%, 0.01% or 0.001% mean in terms of loudness or audibility?

If you are like most people you just know that 0.001% is the best of the three numbers listed above. If you are a well-trained geek you will recognize that each added leading zero represents a 20 dB improvement. 0.01% is 20 dB lower than 0.1% and 40 dB lower than 1%. The well-trained geek will convert % to dB in order to give meaning to these numbers.

When THD is expressed in terms of dB, we can easily determine how loud the distortion will be in our playback system.

Will my audio electronics produce audible distortion?

Will the distortion produced by my audio electronics be inaudible?

- John Siau

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Calculating the Performance of an Amplifier / Speaker Combination - Example 2

Calculating the Performance of an Amplifier / Speaker Combination - Example 2

by John Siau October 27, 2017

Example 2 - PMC MB2S

In this application note we calculate the maximum output level and noise level produced by an amplifier/loudspeaker combination.

This application note can serve as an example for calculating the maximum sound pressure levels and noise output levels for any amplifier/speaker combination.

At the 143rd AES conference in NYC, we demonstrated two Benchmark AHB2 monoblock power amplifiers driving a pair of 4-Ohm PMC MB2S studio monitors.

We were extremely impressed by the unusually clean, distortion-free, output of these monitors. They fully compliment the distortion-free performance of the AHB2 to provide a system with outstanding clarity while delivering high sound pressure levels.

In this application note we will calculate the peak SPL produced by this system. We will also calculate the acoustic noise at a distance of 1 meter from each monitor. We will also discuss some of the unique design features of the MB2S monitors that contribute to their impressive performance.

- John Siau

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AHB2 Tri-Amp Setup - Ellery Coffman

AHB2 Tri-Amp Setup - Ellery Coffman

by Benchmark Media Systems July 27, 2017

The following photos and system descriptions were provided to us by one of our customers, Ellery Coffman. He has put together an amazing system and has carefully treated his room with acoustic absorbers. Nicely done!

Hi Rory,

Thanks again for your help.  For two speakers, it is truly unbelievable how real this tri-amp system sounds; it is nothing short of jaw dropping! It truly sounds better than the $200k+ setups I've heard in some of the high-end audio shops I've been to.

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Speaker Sensitivity and Amplifier Power

Speaker Sensitivity and Amplifier Power

by John Siau April 27, 2017

Speaker sensitivity is a measure of how loud a speaker will play at a given input power or at a given input voltage. Sensitivity is normally measured with a 1 watt power input or a 2.83 Vrms voltage input.

There have been many different speaker designs over the years and there are vast differences in speaker sensitivity. The speakers below have sensitivities ranging from about 85 dB to 109 dB.

  • What are the power requirements?
  • What are the implications for system noise?
  • How loud will each play?
  • Do they require different amplifiers?

- John Siau

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Audio Myths - The Ultimate

Audio Myths - The Ultimate "Myth Buster" Video - Monty Montgomery, Xiph.Org

by John Siau March 14, 2017

Digital Show & Tell, Monty Montgomery, Xiph.org

Monty Montgomery takes us into the lab and uses a series of simple demonstrations to bust some very common myths about digital audio. Test your knowledge of digital audio. This video is fun to watch and easy to understand! Monty takes some difficult concepts and demonstrates them in a clear and simple manner.

Have doubts about Nyquist? Have a fear of stairsteps? Are you worried about ringing? Ever wonder what digital audio does to the timing of transients? This video is for you!

Myth- "Digital audio has stairsteps." 

Myth- "Increased bit depths reduce the stairsteps." 

Myth- "Analog tape has more resolution than digital audio." 

Myth- "Dither masks quantization noise." 

Myth- "Signals lower than one LSB cannot be reproduced." 

Myth- "Digital filters make square waves and impulses ring." 

Myth- "Digital systems cannot resolve timing between samples."

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Intersample Overs in CD Recordings

Intersample Overs in CD Recordings

by John Siau February 10, 2017

Intersample Overs are a Common Occurrence in CD Recordings

We have frequently used Steely Dan's Gaslighting Abbie from Two Against Nature in our listening tests. This is a spectacular CD recording with lots of dynamics and a low noise floor. Nevertheless, in a little over 5 minutes, this track has 559 intersample overs on the left track and 570 on the right track for a total of 1129. This means that there are about 3.7 intersample overs per second. The highest intersample over measures +0.8 dBFS. The track itself is not clipped, the 44.1 kHz sampling has simply captured peaks that exceed 0 dBFS. The following image shows the track with the intersample overs highlighted in red:

This track can be played cleanly by the Benchmark DAC2 and DAC3 converters. These converters accurately render the intersample peaks that were captured in the recording process. In contrast, conventional converters will clip each of the peaks highlighted in red. In this track the peaks coincide with hits to the snare drum. Converters that clip these peaks add a false brightness to the snare drum and alter its sound.

- John Siau

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A Look Inside the New ES9028PRO Converter Chip and the New DAC3

A Look Inside the New ES9028PRO Converter Chip and the New DAC3

by John Siau November 14, 2016

ES9028PRO D/A Converter Chip - Block Diagram and Test Report

This application note examines the differences between the ES9018 and the new ES9028PRO. It also compares the Benchmark DAC2 and DAC3 to demonstrate the performance improvements that can be achieved in a commercial product. It has been a little over 7 years since ESS Technology introduced the revolutionary ES9018 audio D/A converter chip. This converter delivered a major improvement in audio conversion and, for 7 years, it has held its position as the highest performing audio D/A converter chip. But a new D/A chip has now claimed this top position. Curiously the successor did not come from a competing company; it came from ESS. On October 19, 2016, ESS Technology announced the all-new ES9028PRO 32-bit audio D/A converter. In our opinion, ESS is now two steps ahead of the competition!

- John Siau

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Calculating the Performance of an Amplifier/Speaker Combination

Calculating the Performance of an Amplifier/Speaker Combination

by John Siau November 01, 2016

Example 1 - PMC IB2S

In this application note we calculate the maximum output level and noise level produced by an amplifier/loudspeaker combination. Use this example for calculating the performance of your system.

At the 141st AES conference we demonstrated two Benchmark AHB2 monoblock power amplifiers driving a pair of 4-Ohm PMC IB2S studio monitors. These monitor are also available the PMC IB2SE hi-fi version.

In bridged mono, the AHB2 can deliver over 518 watts into each of these 4-Ohm speakers. This is a perfect match to PMC's 500 watt recommendation. The AHB2 easily provides the power, the output current, and the damping required by these low-impedance speakers.

"I am very impressed with the clarity and accuracy of these outstanding professional monitors. The Benchmark AHB2 and PMC IB2S are an absolutely killer combination!" 

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

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Power Amplifiers - A

Power Amplifiers - A "First Watt" ABX Test

by John Siau September 27, 2016

 In Benchmark's listening room we recently demonstrated the importance of the first watt using two 100 watt stereo power amplifiers. One amplifier was a traditional class-AB amplifier, the other was Benchmark's AHB2 power amplifier with feed-forward error correction. Using a double-blind ABX test, we verified that there was a clearly audible difference when the amplifiers drove speakers at an output level of 0.01 watt.

- John Siau

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Audio Myth - Balanced Headphone Amplifiers are Better

Audio Myth - Balanced Headphone Amplifiers are Better

by John Siau September 15, 2016

THIS MYTH GOES SOMETHING LIKE THIS:

"Balanced headphone amplifiers are better."

"If balanced line-level connections work well, balanced headphone outputs should also work well."

We disagree!

Benchmark does not offer balanced headphone outputs on any of its products. The reason for this is that a voltage-balanced interface serves no useful purpose when driving headphones. The truth is that a conventional single-ended headphone drive is technically superior to a balanced drive. This paper explains why single-ended headphone amplifiers are inherently more transparent than balanced headphone amplifiers.

-John Siau

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Inside the DAC2 - Part 3 - Power Supplies

Inside the DAC2 - Part 3 - Power Supplies

by John Siau July 13, 2016

The Benchmark DAC2 is an audio digital-to-analog converter. This application note explains the power supply configuration inside Benchmark'sDAC2 D/A converter. Inpart 1 of this series we discussed the importance of the analog section of an audio converter. In part 2 we discussed the unique high-headroom digital processing chain inside the DAC2. The analog and digital systems each contribute toward Benchmark's overall goal of transparent musical reproduction, but this goal can only be reached when these systems are supported by a well-designed power supply system. In many cases, classic solutions (linear power supplies, line-frequency transformers, and large banks of capacitors) fail to deliver adequate performance. The DAC2 takes a radically different approach.

- John Siau

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Inside the DAC2 - Part 2 - Digital Processing

Inside the DAC2 - Part 2 - Digital Processing

by John Siau June 24, 2016

The Benchmark DAC2 is an audio digital-to-analog converter. This application note explains the proprietary digital processing inside Benchmark's DAC2 D/A converter. In part 1 of this series we made the case that 90% of the components in an audio converter are analog, and that about 90% of the "magic" happens in the analog processing. Nevertheless the 10% that is digital still makes an audible contribution to the sound of an audio D/A converter. This is especially true when the digital processing is complemented by a very pure and clean analog section. With a highly transparent analog section, some of the subtleties of the digital processing can become apparent.

Take a tour of the digital processing chain in the DAC2.

 

- John Siau

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Inside the DAC2 - Part 1 - Analog Processing

Inside the DAC2 - Part 1 - Analog Processing

by John Siau June 04, 2016

The DAC2 is an audio digital-to-analog converter. Most people focus on the word "digital" and assume that all of the "magic" happens in the digital processing, but nothing could be further from the truth! A look inside most audio converters would show that about 90% of the components are analog!

This application note takes a look at the analog processing in Benchmark's DAC2 D/A converter.

- John Siau

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