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.