Subject: [linux-audio-user] documentation; Loudness by Ron Parker
From: R Parker (rtp405_AT_yahoo.com)
Date: Tue Aug 17 2004 - 14:43:23 EEST
Hi,
The recent discussions concerning documentation
motivated me to write an article about mastering. This
document isn't an application or library specific
howto. I'd like to thank Daniel James for editing this
version.
To a small degree my document is a response to Rip
Rowan's Over The Limit article. Over The Limit was
referenced during a thread in which I requested
assistance for achieving maximum loudness. Rip's
article can be found here:
http://www.prorec.com/prorec/articles.nsf/articles/8A133F52D0FD71AB86256C2E005DAF1C
After I'm satisfied with Loudness, I intend to publish
an article on mixing. That document has been sitting
on the back burner for many months. I've just never
presented it.
My document is titled Loudness. The current version is
good enough to publish but I know feedback from our
community will make it better. Where it's appropriate
I will rewrite Loudness.
ron
Loudness
by Ron Parker
This document is a definition of loudness in
mastering, and an introduction to techniques for
solving the basic problem. I'm including quotes from
two letters as arguments in favour of loud mastering.
The album
referred to in the first review is a job for which I
requested advice for techniques to achieve loud
mastering on the Linux Audio User mailing
list. For some of us, the ensuing thread concluded
that loud mastering is bad.
"Just heard the new CD. This is a phenomenal piece of
work. The recording is very crisp and bright. Top of
the heap. First rate! No kidding, this sounds much
better than the majority of my CDs. It's like my
stereo was designed to play it." The job order that
caused this "loud" master basically stated, achieve
every bit of loudness that you can get. And I did!
After completing the above album, I engineered, mixed
and mastered the audio for an eight minute art film.
To design an appropriate mix and master, it was vital
to know that the final destination format is DVD-Video
and the venues for playback vary from 500 seat
theatres to art center installation rooms that fit a
couple dozen people.
After asking numerous questions I concluded that the
quality of playback systems would range from great to
junk. Based on these insights, I designed a mix that
lends itself to loud mastering. By minimising
dynamics and carefully controlling total bass energy
the level of the average soundfloor could be easily
increased to produce a loud master. My reasoning is
that low volume playback on garbage systems will lose
an appreciable amount of information. And the client
review:
"Doctor, GOOD JOB ON THE FILM PROJECT
SOUNDS GOOD ON OUR SYSTEM.....
NICE BRIGHT & CLEAR NOTES
SHOULD SURVIVE <production house name>"
NOTE: Unlike the album review, the film hasn't hit the
streets and passed the acid test. I won't know for a
couple months but fully expect a dozen attendees
crammed into the corner of a room, listening to a boom
box playback system, to hear every single note of the
audio track while a raging orgy of ecstatic wine and
cheese tasters go bananas in the background.
It's my opinion that to claim loud mastering is bad is
the posturing of audio engineers that don't understand
the task. In my experience, loud mastering is a style
that is the perfect solution for specific challenges.
The film track is an example of a job that requires
loud mastering.
TECHNIQUES FOR CONTROLLING LOUDNESS
I'm defining Mastering as having the single objective
of controlling loudness. The challenge is to increase
the level of the average sound floor for any mix.
Assume you have ten control room mixes that aren't
loud enough, and that each of them has a max peak of
-10.0dBfs. The first opportunity is to increase peaks
to 0.0dBfs. JAMin and every other mastering solution
have numerous gain stages; input, EQ, compressor,
limiter, boost/softclip, output.
The +10dB of input gain produces a max peak of
0.0dBfs, but this only begins to exploit the potential
loudness. The opportunity is in creating headroom so
the level of the soundfloor average can be increased
towards 0.0dBfs. The peak is the loudest frequency
while the average is the max response level for the
majority of the frequency range. How to describe this:
Peak - 0.0dBfs
Average - ------- -20.0dBfs
Frequency 20Hz---------20kHz
In the audible range of 20Hz to 20kHz, our example
mixes have a dominant frequency peak from 250Hz to
500Hz. According to our graphic, when 250-500Hz is
peaked at 0.0dBfs, every other frequency is at
20.0dBfs.
If equalisation is used to adjust 250-500Hz by
10.0dBfs the gap between the peak and the average
becomes 10dB. To close the gap even further we can use
the low range band of a compressor to apply a 10:1
ratio.
This creates a new average peak at -20.0dBfs. We've
got 20dB of headroom and all of the aforementioned
gain stages can be used to move the average closer to
0.0dBfs. Now we've got incredible loudness. Obviously,
real mixes have numerous "errant" frequency bands.
MULTITRACK SOURCES
The advantage of multitrack sources is a level of
control that isn't available when working with stereo
files. Even though good mixes don't require a great
deal of tampering, common problems are discovered and
easily fixed during mastering. Regardless, there is a
serious limitation; it's difficult beyond reason to
put 10 multitrack sources within one session file, and
mastering is the task of making many songs sound great
together.
Consider a multitrack source where the snare drum is
the loudest instrument and it has +6.0dB transient
peaks. When this mix is routed to a stereo bus which
in turn routes to JAMin the instrument controlling the
potential level for the average soundfloor is the
snare drum. When the LADSPA TAP Limiter is used to
eliminate the +6dB spikes on the snare track the
resulting average soundfloor (entire mix) can be
increased +6.0dB without causing clips.
Assuming low frequency energy below the audible range
of 20Hz is a cause for peak levels, the Jack Audio
Analyser can be used to examine individual tracks for
excessive energy and equalisation can be adjusted.
Imagine three instrument tracks where -3.0dB
equalisation cuts in the low frequency ranges around
20Hz create an accumulated 9.0dB of headroom without
having a negative effect on the sound quality. The
resulting average soundfloor is a much better mix for
the mastering engineer.
These examples are far from reality but they describe
what mastering is and how to use a typical set of
tools to achieve the greatest potential for loudness.
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