I’VE SEEN SEVERAL COMMENTS
online that amp sims are okay for distorted
sounds, but not clean ones. However, it’s
very easy to get good, clean guitar sounds,
sometimes even with that “tube sparkle”
. . . you just have to know these six secrets.
1. Record at an 88.2 or 96kHz sample
rate. The lack of “cleanliness” you hear
might not be due to excessive levels that
cause clipping, but aliasing or foldover distortion.
Recording at a higher sample rate
minimizes the odds of this happening (note
that several guitar amp sims offer an “oversampling”
option that accomplishes the
same basic result, even if the project’s base
sampling rate is 44.1 or 48kHz).
2. Choose the right amp model. This
may seem obvious, but not all clean models
are as expected. For example, many
“clean” emulations have a little bit of
crunch, just like the original. Some sim
manufacturers create clean amps that aren’t
designed to emulate classic amps (Figure
1); try these first.
Figure 1: AmpliTube 3’s Custom Solid State Clean model doesn’t have to emulate anything, so it’s designed to be as clean as possible.
3. Turn down the drive, turn up the master.
It’s possible to get cleaner sounds with
some amp models by dialing back dramatically
on the input drive control, and boosting
the output level to compensate (Figure 2).
Figure 2: POD Farm 2’s Blackface Lux model can give clean sounds that ooze character. Here’s how: Turn down the amp Drive and input gain, turn the amp Volume all the way up, and set the output gain high enough to give a suitable output level.
4. Compress or limit on the way into
the amp. Building on the previous tip, if
you’re pulling down the level, then the guitar
might sound wimpoid. Insert some
compression or limiting between the guitar
and amp model to keep peaks under
control, and allow getting a higher average
level to the amp without distortion.
5. Watch your headroom. Guitars have a
huge dynamic range, so don’t let the peaks
go much above –6 to -10dB if you want to
stay clean. Yes, we’re used to making those
little red overload LEDs wink at us, but
that’s not a good strategy with digital
audio—especially these days, when 24-bit
resolution gives you plenty of dynamic range.
6. Beware of inter-sample clipping. With
most DAWs, you can go well into the red
on individual channels because their audio
engines have virtually unlimited headroom
(thanks to 32-bit floating-point math or
better, in case your inner geek wondered).
However, when those signals hit the output
converters to become audio, headroom
goes back to the real world of 16 or 24 bits,
and any overloads may turn into distortion.
Figure 3: Waves’ G|T|R is set to a clean amp. The DAW’s master output meter (left) shows that the signal is just below clipping, but SSL’s X-ISM meter that measures inter-sample distortion shows that clipping has actually occurred.
So if the meters don’t show clipping you’re
okay, right? Not so fast. Most meters measure
the actual values of the digital waveform’s
samples, prior to reconstruction into analog.
But that reconstruction process might create
signal peaks that are higher than the samples
themselves, and which don’t register on your
meters (Figure 3). Fortunately, you can download
SSL’s free metering plug-in that shows
inter-sample clipping from www.solidstatelogic.com/music/X-ISM/index.asp.