Improve Amp Sim Tones Instantly

November 1, 2009

HERE’S AN EASY WAY TO IMPROVE AN AMP simulator’s tone dramatically: increase the sample rate at which it operates. Now, I’m not some golden ears guy who insists that recordings done at 96kHz sound sooo much better than a CD’s standard 44.1kHz sample rate, but amp sims are a special case—especially at high-gain settings.

The sample rate is the rate at which audio is converted to digital data. The faster the rate, the more accurate the conversion—just like how videos that show more frames-per-second give smoother visual motion. With most audio sources, 44.1kHz is an adequate sample rate. But overdriven/high-gain amp sims generate harmonics that can extend beyond the highest audio frequency a digital system was designed to handle. This causes aliasing—a term for what happens when the harmonics interact with the digital system’s sample rate. The audible results are noise, atonal harmonics, and a blurred, often harsh sound. Raising the sample rate helps minimize interaction with the harmonics. Here’s how…

First, set your audio interface to 88.2kHz or 96kHz (most current interfaces support these rates). Then, open an amp sim in standalone mode, and set its sample rate to match your interface (Fig. 1). You should hear much sweeter high-gain sounds. This isn’t just due to less aliasing. It’s also because the filters that are an essential part of digital-audio conversion don’t have to work as hard, and can sound more natural.

You don’t get something for nothing, though. Higher sample rates stress your computer more, so you may have to increase the system latency to avoid audio dropouts. Fortunately, with today’s fast multi-processor systems, this is becoming less of an issue.

When using an amp sim as a DAW plug-in, it may not be possible to run at higher sample rates with complex projects. For example, some other plug-ins might not work properly at 96kHz, and the demands on your computer might be excessive. One solution employed by IK Multimedia and Native Instruments is to include optional oversampling in their amp sims (Fig. 2). This runs the amp sim at a higher internal sampling rate than the project itself, giving the benefits of a higher sample rate— even in projects running at 44.1kHz or 48kHz. Oversampling places more of a load on your CPU, but far less than doubling the sample rate of an entire project. If you can’t raise a project’s sample rate, check for places in amp sim programs where you can enable oversampling— your ears will thank you, because the overall sound will be much more like a real amp.

Major props to Davide Barbi at IK Multimedia and Patrick Arp at Native Instruments for providing helpful background material.

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