Keeping it Clean in the Digital Domain

Digital means clean, right? Well, I wish . . . but there are plenty of digital gremlins who are ready to rise up and bite you if you’re not careful.
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One way to help keep a digital track clean is to stay in the digital domain once the track is recorded. Each time a signal passes through converters and into outboard electronics, the sound changes — however subtly — and some noise hitches a ride. If an outboard processor adds to the track, or if you prefer to mix via analog summing, go ahead: But know what you’re doing and why, listen to it both ways, and make an informed decision. If your signal path can live without an extra stage, don’t use it.


Suppose that for the most part your recording is clean, but there are a few remaining noise issues. Do you grab a noise reduction plug-in? I avoid them unless absolutely necessary, and when I do need noise reduction, I use the bare minimum. Noise reduction works by subtracting energy in particular bands, and when pushed too hard, they may subtract energy you do want. Besides, the sonic artifacts from even the best noise reduction algorithms can sound more distracting than the noise. If the noise is really bad, it’s re-recording time.


Not all noise is electronic. While tracking one of the songs on Julie Day’s CD (, we could hear the upright bass buzzing. First we thought it was from a humidifier that was accidentally left inside the bass and sympathetically vibrating as the instrument was played, but even after removing it, there were still places where the bass would buzz, and we couldn’t locate the problem to fix it. As we had several other musicians waiting and the clock was ticking, we just went ahead and tracked anyway, figuring we’d fix it later.

Well, it wasn’t easy. When we found an objectionable note, we searched the tracks until we found the notes we needed (with the proper pitch and inflection but without the buzz) from elsewhere in the song or from alternate takes, and flew them over to replace the bad notes. There were so many spots with buzzes on that song that the majority of notes had to be edited. Doing that takes forever, and you have to be pretty good with your editing chops if you are going to sneak that past your listeners. Of course, if things are that bad, retracking is usually the better answer, but sometimes you have to do what you have to do.


Here are some other tips that can help at mixdown.

n Listen to each instrument and roll off any unnecessary bottom with a steep high-pass filter. If there is nothing but room rumble and air conditioning noise down below 100–150Hz on a track, filter it out. This one step will make a huge difference in cleaning up a muddy mix, as well as reduce any subsonics that snuck their way into the track.

n Some soft synths have high-resolution or “low aliasing” modes that suck more CPU, but reduce artifacts. Use them! If your computer can’t handle the load, freeze the track.

n If an instrument doesn’t have much going on in the upper frequencies but noise and hiss, try a low-pass filter or a bit of high frequency shelving EQ to pull back the noise. Remember that most EQs can be automated, so you can open up the response if highs are present.

n Although you can trim individual regions to “remove silence,” you can also use mute or fader automation to turn off tracks when they’re not needed. In Figure 1 there’s noticeable headphone bleed from the vocal track during a sax solo, so I used volume automation to bring the faders down in the spots where there weren’t any vocals to mask it. However, don’t go too far — some breaths and “humanisms” should be left in the mix, but control them and their levels as needed. (You can hear a “before and after” example of the soloed lead vocal in Figure 1’s highlighted section at

The bottom line is whenever possible, avoid noise issues at the source rather than try to correct them later. It usually takes less time and provides better results. But don’t go too far over the top and kill the music; a little dirt once in a while isn’t going to hurt anything — but a lack of vibe most certainly will.