What is a Dorrough meter? An intro to Dorrough loudness metering
There’s somewhat of a hall of fame of classic, iconic metering gear.
If you’re an audio engineer, you’ve probably developed some sort of relationship with your favorite meters. Every engineer has their preferences. Is the Dorrough meter one of the pieces you swear by?
The Dorrough meter has earned its place among the classic metering tools, particularly in broadcast, where it has been used for decades. But what exactly makes the Dorrough loudness meter different from other approaches to level metering?
Let’s take a closer look at this iconic piece of gear, how it works, and why it remains relevant today.
Curious about how the Dorrough meter would look in your own workflow? We’ve built three classic models into our latest release. Try our Dorrough meter for free:
What is the Dorrough meter?
Michael Dorrough is a legendary engineer who created a series of loudness meters under the Dorrough Electronics brand.
The original Model 40, followed by the later 280 and 380 models, are all loudness meters designed to monitor the average energy content of an audio signal alongside simultaneous real-time peak level monitoring.
Dorrough felt there was a problem with metering at the time he was developing his signature pieces. He believed that the two main metering standards, VU (Volume Unit) and PPM (Peak Programme Meter), created an issue in that different approaches to broadcast metering had developed across the US and Europe.
On the one hand, he called out the VU’s flaws, feeling that it was quite a rudimentary piece of gear. He even went as far as calling the VU meter “quasi-average” in his official documentation. The classic VU meter was designed to give engineers an indication of average program level, using a 300 ms integration time to smooth out fast transients. This makes it useful as a rough representation of average energy and perceived loudness, but it also means that short, fast peaks can disappear from view.
While he held that PPM addressed some of the issues that the VU posed, his problem with PPM was that it focused mainly on the peak level of the waveform, without giving you the same immediate picture of its average energy.
Dorrough asked whether it was possible to see average and peak information at the same time. Having both pieces of information available at once allows you to see how loud a signal is and, critically, how its peaks relate to its average level.
They say necessity is the mother of invention. In this case, necessity led to the invention of the very first Dorrough meter.
When was the first Dorrough loudness meter created?
Following the early success of the DAP (Discriminate Audio Processor) in the early 1970s, Michael Dorrough created the Model 40 loudness meter in 1980. This was designed to fill the gap that Dorrough had identified, as the Model 40 was able to simultaneously show peak and average levels in a single display.
In this video, you can see a classic Model 40 pair in action:
Years later, shifting standards in audio formats meant there would have to be iterations on the classic.
What’s the difference between the various Dorrough loudness meters?
Focusing on the 40, 280, and 380 models, let’s break down the differences between them:
Model 40
The original Dorrough loudness meter. This model features two distinct arc-shaped loudness scales. In standard practice, each meter would typically measure the left and right channels. They could, of course, be configured to capture data from various incoming mono signals as well. The Model 40 was designed for analog audio, which is where its successors come in.
The Dorrough Model 40, recreated digitally
Models 280 and 380
Moving into the digital age of audio in the early 1990s meant the Dorrough hardware had to develop with the times. Enter the 280 and 380 Dorrough audio meters. While they provided the same basic functionality as the original Model 40, the new variants were able to accept digital data signals and display two channels on the same unit.
The main difference between these two models comes in how they’re mounted, with the 280 designed for horizontal display and the 380 for vertical display. Both models also came with different scale options: 40 dB and 60 dB.
The Dorrough 280, recreated digitally
It's also worth remembering that these meters came from an analog and broadcast world, where calibration was tied to electrical operating levels rather than the dBFS scales we're used to seeing in modern digital audio.
Dorrough meters were manufactured in different variants, including the 40-A and 280-D, with calibration options for different music and broadcast applications. Professional line-level conventions such as +4 dBu were part of this world, alongside alignment references based around 0 VU in analog workflows.
This is all to say that the numbers on a classic Dorrough meter aren't simply a digital representation of how close your signal is to 0 dBFS. They're tied to the operating levels and calibration conventions of the equipment and environments these meters were designed for.
How do you read a Dorrough meter?
So, what are you actually looking at on a Dorrough meter?
A Dorrough meter gives you two simultaneous readings on its LED scale. One tracks peak excursions, while the other follows average level. Seeing both at once gives you a much better picture of what's happening dynamically inside your audio.
You might wonder, then, what’s going on in the space between these two readings. Herein lies the magic of the Dorrough meter.
Mind the gap: the relationship between peak and average levels
If there's a large gap between the peak and average levels, you're looking at a signal with a high crest factor and therefore greater dynamic range. This might be a signal with prominent transients, for example. If the two readings sit close together, the signal is more dense, which could be the result of compression, limiting, or simply the nature of the material itself.
You can also use the relationship between the two readings to get a quick sense of what's happening dynamically. If the peaks are getting close to the top of the scale while the average level remains relatively low, you've got a transient-heavy signal. On the other hand, if the average level is sitting high and the peaks are tightly constrained, you're probably looking at more aggressive dynamics control.
Is the Dorrough meter dead?
While Dorrough Electronics itself seems to have gone quiet, there are still many engineers out there who swear by their Dorrough meters.
The interview below is a testament to the fact that people still love their Dorrough audio meters, praising how you “can identify the density of processing as opposed to just loudness,” and “how close [you can identify] from average meter versus the peak.”
If you’re interested in going in depth, catch this conversation on GFQ Network with Michael Dorrough:
The iconic Dorrough meter may be somewhat niche nowadays, but it is being kept alive in both hardware and more modern formats.
Dorrough meter plugins in DAWs
Getting your hands on a classic piece of Dorrough gear might well end up costing you an arm and a leg. That’s assuming you can even find one in good working condition. As we’ve discovered, the engineers who are lucky enough to have one wouldn’t want to let theirs go. That’s why Evergreen Audio decided to make the Dorrough meter more accessible than ever.
Understanding the general reverence that engineers have for this meter, we decided to pay our respects too. Our latest update to Massive Meter Pro features meticulously crafted replicas of the 40, 280, and 380 models. That means it’s now easier than ever to access this classic workflow. You can also escape the limitations of physical gear, as you can integrate as many instances as you need right into your DAW.
Try the legendary Dorrough meter for free
Bringing this iconic piece of gear into a modern workflow is one of the fantastic privileges of working in audio in the digital age. Experience the Dorrough meter with Evergreen Audio. Try it for free yourself, and see what all the fuss is about:
