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Why Specifications Matter | Part 1: Spec Sheets

On Specs

Specifications can be a useful guide when choosing equipment. Our new series, in association with Audio Precision, explains how to understand and compare the specs of competing products.

Credible audio‑equipment and electronic‑component manufacturers prepare product specification sheets with proper attention to accuracy. Manufacturers tend to be as forthcoming in their spec sheets as their competitive markets require. Yet when purchasing end‑user equipment, customers — even relatively tech‑savvy ones — can find various specs and different expressions for similar quantities confusing. This can make side‑by‑side comparisons of competing gear difficult and frustrating.

Judgement Days

When a company launches a new product development program, the internal spec sheet defines that product — its features, capabilities, and performance characteristics — to project contributors and stakeholders. Prior to product release, engineering and technical marketing staff will prepare a subset of the internal spec for release as a customer‑accessible verified product spec sheet that identifies what purchasers can expect of the product.

In this fashion, one of the important roles a spec sheet fulfils is as a detailed expression of a product’s value proposition: an account of what you’re getting for your money. Knowing how to glean information from its tables, charts and graphs allows you to better assess a product’s attributes, not just in absolute terms but also in the context of your specific interests.

For example, if you record spoken word projects such as podcasts, lectures, tutorials and audio for video, or acoustic music performances, you might value a mic preamp that features higher maximum gain and lower noise compared to a competing device. By contrast, if you’re making death metal tracks, mic pre gain range and noise performance are less likely key concerns, because a lack of signal amplitude isn’t going to be your problem. Other characteristics will likely occupy top spots on your must‑have list.

Learning your way around various spec expressions equips you to correctly compare product performance in an absolute sense. Understanding the behaviours and traits behind the numbers enables you to assess performance claims in the context of your particular needs and interests.

There are some performance specifications that appear to quantify with a single value what is, in fact, complex multi‑parametric behaviour.

Terms & Conditions Apply

There are some performance specifications that appear to quantify with a single value what is, in fact, complex multi‑parametric behaviour. In these cases, the phrase “terms and conditions apply” is a handy one to keep in mind. Before comparing a spec on competing products, check that both spec sheets express the measure in the same terms, and that they specify the behaviour under the same operating conditions.

For example, power amplifiers’ output power specifications don’t have meaning unless they’re accompanied by a stated distortion limit and load impedance. Amp makers virtually always express the output power rating in Watts, so having matched terms in this case is pretty much a given. But if one amp’s output power spec assumes an 8Ω load and a competitor assumes a 2Ω load, the numbers aren’t directly comparable, because the operating conditions don’t match.

Similarly, meaningful output power specs must identify what the manufacturer has chosen as the maximum level of distortion. An amp specified with a maximum output of, say, 100W at 1% distortion may be a better choice than one rated at, say, 135W at 5% distortion if your interest is high‑quality audio presentation. But the opposite might be true if you’re selecting an amp to, say, drive the PA at a supermarket.

The Standard Drill

With the many specifications one can list for any piece of audio equipment and the huge number of possible choices for test operating conditions, a situation could easily exist where every manufacturer chooses their own favourite combinations, making direct comparisons extremely difficult if not impossible. This is where test standards can establish agreed‑upon spec definitions, test conditions and measurement procedures to yield consistent, repeatable and comparable test results.

Seemingly disparate organisations have developed a remarkable array of standards for audio applications. Some of these standards publishers are geo‑centric, like the IEC (International Electrotechnical Commission) and DIN (Deutsches Institut für Normung). Others are application‑centric, like the SMPTE (Society of Motion Picture and Television Engineers) and the EBU (European Broadcasting Union). Still others, like the AES (Audio Engineering Society), have broad interests in audio and draw from experts with wide‑ranging backgrounds.

Less common, but worthy of note, are governmental agencies, which can regulate how equipment providers express certain specs (including reporting of test operating conditions) for listed gear selling into identified markets. An example is the FTC’s (Federal Trade Commission’s) Amplifier Rule Title 16 Part 432, which regulates output power claims in audio power amplifier advertising within the United States.

Since the end of the last century, the trend in technical standards across many industries has been to harmonise, or converge, specs covering the same topics for similar applications. This behaviour recognises that many equipment suppliers sell into a global market, so large savings accrue to those who can sell the same design across multiple territories or applications. This trend also benefits customers, because it increases the likelihood that individual specs will be comparable for competing equipment even if sourced from companies based in different countries. Greater choice usually implies greater competition.

When navigating equipment specification sheets, you don’t need to know the details and requirements of quoted standards. You can consider standards as abstractions that ensure consistent spec expression, operating conditions and measurement methods for the parameters they cover. While you don’t need to know the detail under the abstraction, you do need to confirm, when comparing competing devices, that both products’ spec sheets refer to the same standard. Also note that standards evolve over time, so you want to be sure that the standard quoted in both cases is of the same revision or release date.

With thanks to Dan Knighten, Product‑Line General Manager at Audio Precision Inc.