Excerpt from Clean Audio Installation Guide: System Frequency Response

In 1986, the founder of Benchmark Media Systems, Inc., Allen Burdick (since-retired), wrote an application note titled "Clean Audio Installation Guide". The paper began circulating among engineers at broadcast facilities and recording studios. Eventually, engineers at major facilities were personally thanking Mr. Burdick for this comprehensive guide to audio system deign and installation, and began regarding the paper as "required reading" for audio engineers. More then 22 years later, engineers are finding the topics in this paper more relevant then ever.

Here is an excerpt of the "A Clean Audio Installation Guide." This section explains the importance of wide bandwidth components in an audio system. To download and read the entire Clean Audio Installation Guide", click here.

Excerpt from "Clean Audio Installation Guide":

3.5 System Frequency Response

All of the (previous discussions) assumes a 30 kHz interconnect full voltage (slew rate) capability. This is our recommendation for minimum system performance. It is also our firm recommendation that a 200 kHz small signal interconnect bandwidth capability be the design goal to achieve the flattest response and minimum phase shift at high frequencies for good overall system performance.

It is important to recognize the difference between the small signal bandwidth of an interconnect and its slew rate limitations.

Small signal bandwidth sets the 3 dB cutoff of the interconnect filter, which in turn describes the flatness and phase response back at 20 kHz. It must be remembered that every element of an audio system will contribute it's 3 dB cutoff and associated phase shift to the overall performance of the system. Every element must be viewed as one section of a large multi-pole low pass filter; and while one element may have adequate response to 30 or 40 kHz, it is the cumulative effect of these filter sections that is of major concern. At first glance, the proclaimed need for a wide bandwidth of 200 kHz in both the equipment and the interconnect may seem outlandish. However, when you realize that the audio may travel through five, ten, twenty or even more pieces of equipment in the audio chain, each contributing its cutoff characteristics, we begin to realize the magnitude of the problem in achieving adequate high frequency performance through the entire system.

If a piece of equipment or an interconnect has a 100 kHz bandwidth and has a simple single-pole, 6 dB per octave roll off (often only true for interconnects), the following chart can be used to estimate the system roll off.

Manufacturers of audio equipment have for years mistakenly considered an upper bandwidth of 20 to 30 kHz to be totally adequate for their equipment. This narrow viewpoint, of course, fails to see their equipment as an element in a long chain, and potentially the limiting element. While we will actually never "use" - that is, put a signal into that upper portion of the 200 kHz bandwidth - it must exist to achieve the necessary 30 to 40 kHz system bandwidth.

We have often been told that "an audio chain is only as strong as its weakest link." However, in the case of audio systems, each additional link makes it weaker then its weakest link. In fact, a better analogy may be several layers of tinted glass. Even a highly transparent layer of glass will further reduce the total light emission.

Slew rate limitations, on the other hand, are large voltage swing limitations and again, have to do with the actual current output required of a stage that is driving a capacitance. It is important that no amplifier be allowed to slew limit. To do so produces high frequency intermodulation distortion. If an amplifier can provide adequate current to a cable to allow full output swing to 30 kHz at low THD, the chances are practically nil that it will ever slew limit with normal audio.