An example of a
digital meter that was designed to display both VU standard response
and peak tracking.
articles have appeared lately on the history and use of audio level
meters in radio, including Oliver Berliner’s “The
‘vu’ Meter Legacy Shines On”
in Radio World’s May 8 issue. However, these articles have not
addressed one important modern issue: We now have studios full of
meters that do not respond in the same way on dynamic program
material, and which do not follow the VU and PPM standards for
I would like to
describe the situation and offers suggestions for getting along with
this modern metering.
WHY DON’T THE
Once upon a time in
our business, if you calibrated all the meters in a studio to agree
on a steady tone, they would also agree on voice and
music. Unfortunately, those days are gone. In the days of
analog meters and recording media, a “vu meter” had a technical
specification as to performance on a variety of audio, and you could
count on vu meters all bouncing to the same levels on the same
signals, resulting in a consistent level being observed from console
to console and among recording and playback devices.
In other words, if
you calibrated all the equipment with a standard tone, and everyone
bounced the meters about the same, the results would be fairly
consistent no matter what sort of programming was being produced. The
same was true for facilities equipped with the less commonly used
“PPM” (Peak Program Meter) standard.
But today, you can’t
trust that audio level meters are standardized. While they should
ideally all respond to steady tone the same way, in reality, they can
be wildly different on actual, dynamic program material. Some meters
follow momentary peaks while others ignore them — and you will find
all variations in speed of reaction between those extremes. This kind
of variation leads to differing levels on production done on
different equipment with different audio material.
“meters” are a big offender in this regard. The “bounce” of
the onscreen “meters” is very different from real vu meters and
can be misleading, especially on dry voices, resulting in different
announcers getting different results, even when they think they are
making the meters read the same.
In addition, the
varying lag time involved in the calculation and display of the meter
bar graphs in computerized systems can play a big role as humans use
the display for real-time work.
WHAT TO DO?
Audio level meters
should adhere to the official VU standard for response to signals,
but don’t always, even if they are marked ‘VU’ on the face.
Here at Wisconsin
Public Radio, we always calibrate to a standard tone, but I recommend
to our staff that they also look at the overall waveform display when
finished with a recording, in order to learn how to judge the levels
on real program material. I like to see a waveform that occupies
roughly two thirds of the available space. That generally results in
a good level.
And you don’t want
many, if any, instances when the top and bottom of the waveform
limits are reached. Those are peaks, which are getting hard-clipped
because you are out of headroom. With experience, you can learn what
meter bounce on your equipment produces a given waveform appearance,
as well as corresponding loudness on playback for the typical sort of
audio you are recording.
When using import
software to directly transfer files into computerized
storage/playback systems, it is important to do some followup checks
to see how loud or soft the audio is once it gets into the system.
Since people can change the way audio is displayed on their
production software (Sound Forge, Adobe Audition, Audacity, Pro Tools,
etc.) and the digital “meters” on that software vary in
performance, there is no reliable standard between production
software and automation systems for file transfers.
Have a look at the
waveform in your automation after import and note how it compares to
the waveform in your production software. If needed, adjust your
levels using the building in normalization features of the editing
software, resave the file, use the import process again and have
another look. After some quality control comparisons of this sort,
you’ll soon learn what loudness you need on your production system
to get a successful file transfer.
digital recording, what sets the level is how the file ends up on the
recording media, which these days is usually the hard drive in the
device that will be used for playback on the air. Level indicators
and waveforms on recording and editing devices earlier in the
production process, while important for keeping audio clean and free
of clipping on their own device, do not directly control the level
and loudness at which your program material ends up playing back on
variation will always be present. Air studio operators are expected
to use their faders, and we should always have audio processing on
the outgoing audio lines, which will compensate to some degree for
varying levels. But always bear in mind how modern audio level meters
may bounce in differing ways.
Getting a handle on
the wildly varying audio metering is not easy. Orban has produced a
free software package known as the “Orban Loudness Meter”
which accepts two-channel stereo inputs and displays instantaneous
peaks, VU, PPM, CBS Technology Center loudness, ITU BS.1770-2, EBU R
128 loudness, and Reconstructed 8x Over-Sampled Peaks. The comparison
of the various meters shown in the Orban program as you work with
audio in your studio software and hardware can be very educational.
It will help you understand the issue we face.
I have hopes that
the recent interest in metering of the human perception of “loudness”
and projects such as the ITU BS.1770-2 standard (see
to read it) will stimulate enough interest in the subject that
equipment manufacturers will embrace a new standard and we can begin
to trust the meters again.
Steve Johnston is
the director of engineering and operations at Wisconsin Public Radio.