Master Class: Pump Up Your Mix With Free Audio Plug-Ins

How to set yourself up with free mixing and mastering tools, and what to do with them
Image placeholder title

Plug-in signal processing is the mother’s milk of creative in-the-box production. Unfortunately, it can cost big bucks to fill your glass. Thankfully, many manufacturers offer one or more plug-ins for free. I'm not talking about demo-mode free. I mean forever free, with absolutely no time limit or restrictions on use.

This article is your handy guide to some of the best free plug-ins available for mixing and mastering. And while “no cost” usually implies low quality, that’s simply not the case here. True, some of the free plug-ins detailed in this guide are lesser-featured versions of paid plug-ins offered by the same manufacturer. But while the freebies’ capabilities may be somewhat limited compared to those offered by their cutting-edge, commercial counterparts, their sound quality is just as high.

This guide by no means covers all the gratis plug-ins available on the Internet. You’ll find an incredible bounty of freebies online once you start digging. (Better bring a backhoe!) Rather than fill this article front to back with a laundry list of all the software you can possibly hoard, I’ll focus on a core group of products and tell you what you can actually do with them in the studio. Happy shopping!


Fig. 1. The Blue Cat’s Freeware Plug-ins Pack II comprises a lavish offering of free plug-ins, including a flanger, phaser, chorus, 3-band semi-parametric equalizer, real-time spectrum analyzer, and master gain controller. Blue Cat’s Freeware Plug-ins Pack II ( includes six free plug-ins in AAX, AU, RTAS, VST, and DirectX formats and mono, stereo, and (for some of the plug-ins) dual-mono configurations (see Figure 1).

Image placeholder title

Blue Cat’s Chorus includes all the controls you need to create lush chorus effects: delay time, depth, rate, LFO waveshape (sine or triangle), separate level controls for dry and wet signals, and (in the stereo version) a spread control that adjusts the stereo image. But you can also mangle sounds in really cool ways that go way beyond chorusing. For example, by switching the waveshape to triangle, cranking the depth control fully clockwise (to 100 percent), plunging the spread control all the way to mono and killing all dry signal, you can make a stereo synth pad pulse with a rounded at- tack to sound more like an electronic piano than a pad; adjust the rate control to determine how quickly the pulses repeat, making them synch with your song’s tempo.


Blue Cat’s Flanger provides two key controls for adjusting the depth and tonality of its flanging effect: Feedfwd (feedforward) and Feedback. Feedfwd sets the level of the effect’s delayed-signal component. (The Delay control sets the component’s delay time, which is modulated using the Depth and Rate controls.) When combined with the dry signal, the feedforward signal creates a comb filter.

The Feedback control sets the amount of effect signal that’s regenerated (using a feedback loop), adding resonance to the comb filter’s peaks and troughs, and intensifying their effect further. With each control, a setting clockwise from the noon position adds effect signal that’s in phase with the dry signal, while counterclockwise-from-noon settings flip the phase of the effect. Try adjusting either Feedfwd or Feedback—or both—to flipped phase settings to keep resonant bass-frequency peaks under control. To create warbling or downright bubbly, synth-like effects, use very high Rate settings.

The control set for Blue Cat’s Phaser is similar to that for the company’s freebie Flanger but uses a Stages control in lieu of a delay-time control. As you raise the Stages control, you increase the number of phase-shifting all-pass filters used, creating more notches and peaks in the resulting comb filter and intensifying the plug-in’s phaser effect. The Wet control adjusts the amount of directly phased (that is, not fed back) signal.

The Feedback control performs essentially the same level and phase functions as the control by the same name in Blue Cat’s Flanger. To make your guitar gently weep, crank the Stages control to its maximum value, set the Rate knob to around 3.64 Hz, turn off Feedback, and dial in roughly equal settings for the Dry and Wet controls.

Considering it’s a gratis offering, Blue Cat’s Triple EQ is a surprisingly flexible and potent 3-band semi-parametric equalizer. In addition to mono and stereo configurations—and a midside mode for the latter—a powerful Dual Channels configuration is also included on the house. With linking defeated between its two channels, the Dual Channels version can apply equalization independently to each channel. For example, you can boost the low end for the bass and kick (and other elements) in the mid channel of a stereo mix without blurring hard-panned electric guitars. And if one of those guitars is making the left channel sound muddy, you can cut low-midrange frequencies in that channel without affecting the clear-sounding right channel.


A Relative mode lets you link channels while preserving any pre-existing control offsets between them. These are advanced capabilities usually only found in the best equalizers on the market—and they’re yours for free! And when your tired ears can no longer decipher what you’re hearing, reach for the free Blue Cat’s FreqAnalyst. This real-time spectrum analyzer can display instantaneous and peak levels in turn or simultaneously for the left, right, or both channels.

Blue Cat’s Gain offers mono, stereo, and dual-channel configurations. Using its dual-channel form, you can separately control the gain of mid and side channels, for example, to widen or narrow the stereo image of a keyboard track or full mix. Multiple instances of the plug-in (having the same configuration) can be linked and controlled from one GUI. Imagine, for example, linking instantiations of Blue Cat’s Gain placed on all your synth tracks and ballooning the stereo widths of all the tracks at once using one side-channel gain knob!


Fig. 2. Boz Digital Labs’ Bark of Dog is a resonant highpass filter that gives bass instruments like kick drum extra punch. Bark of Dog (AAX, AU, RTAS, VST, VST3), a resonant highpass filter (HPF) from Boz Digital Labs (, gives bass instruments such as kick drum extra punch. Dial in the corner frequency you wish to hype on your track, and adjust the plug-in’s Amplitude control to boost your selected frequency to taste (see Figure 2). All other frequencies below the corner frequency will conditionally be rolled off; if you want to more or less preserve those frequencies, lower the plug-in’s Mix control to add back some dry signal. Use the Trim slider to adjust the plug-in’s output level.

Image placeholder title


IK Multimedia ( is famous for its Custom Shops, online stores that allow you to buy add-ons to expandable pro-audio and musical- instrument software à la carte. The company’s T-RackS Custom Shop offers dozens of mixing and mastering processors, including compressors, equalizers, reverbs, and de-essers.


Fig. 3. IK Multimedia’s T-RackS Custom Shop comes pre-loaded with the free Classic Equalizer and Metering Suite modules, along with demos of roughly 30 other processors you can buy à la carte at the company’s online store. A free basic version of T-RackS Custom Shop comes both as standalone software and a shell for loading up to twelve processors at once—on a track’s insert—in your DAW (see Figure 3). The first eight slots for the processors are arranged in parallel configuration, four slots to each audio path; after submixing the two paths, four more slots follow in series. Along with the T-RackS shell, you get the Classic Equalizer and Metering Suite processors gratis. Around 30 other processors also come pre-loaded and operate in demo mode. All processors can also be instantiated as single plug-ins (AAX, AU, RTAS, VST).

Image placeholder title

Classic Equalizer is a dual-channel affair offering six bands: two of the bands use parametric peaking filters, while the other four bands feature respective low and high shelving and highpass and lowpass filters. You can EQ the left and right (or mid and side channels, in M/S mode) independently or link the two channels to apply the same EQ to both at once.

The T-RackS Metering Suite includes facilities for viewing peak and RMS levels, perceived loudness, phase and spectrum analysis. The perceived loudness meter combines averaging and frequency weighting to arrive at its combined volume display for both channels. Select a music genre (such as Funk Rock) from a pop-up menu to adjust the placement of colored bars underlying the meter; the bars suggest a range of target levels you should aim to achieve in your mastering for the selected genre.


Fig. 4. Plugin Alliance, a consortium of pro audio companies, offers the Brainworx bx_solo and bx_cleansweep V2 (monitoring facilities and sweepable filters), SPL Free Ranger (a modeled passive equalizer), and elysia niveau filter (a tilt equalizer) on the house. Four complimentary plug-ins—collectively from three manufacturers—are currently available from Plugin Alliance (; see Figure 4). The Brainworx bx_cleansweep V2 (AAX Native, AU, AudioSuite, RTAS, TDM, Venue 32-bit, VST2, VST3) offers continuously variable highpass and lowpass filters, each with their own bypass. Use both filters at once to discard boomy lows and brittle highs from electric guitar tracks, sitting them perfectly in the midrange pocket. Feeling more adventurous? Mouse-drag the GUI’s automatable joystick to simultaneously lower both filters’ corner frequencies from their maximum to minimum values and back again; this creates a bandpass-filter sweep that sounds great on full-bandwidth synth tracks and drum subgroups.

Image placeholder title


Every engineer should own Brainworx bx_solo (AAX Native, AU, AudioSuite, RTAS, TDM, Venue 32-bit, VST2, VST3), baby brother to the company’s outstanding bx_control V2 (which, incidentally, I use on every mastering session I do). The free bx_solo lets you solo in turn the left, right, mid, and side channels of your mix to hunt down distortion, clicks, and phase problems. (Hint: If you can hear your sampled kick-drum in the side channel, it’s out-of-phase and robbing your mix of low end.) Swap the left and right channels with one mouse click. Use the Stereo-Width control to widen or narrow full mixes, keyboard tracks, guitar subgroups, and tracks for drum-room mics.

The elysia niveau filter (AAX DSP, AAX Native, AU, AudioSuite, RTAS, VST2, VST3) uses tilt equalization to quickly adjust the timbre of your tracks. First, use the EQ Freq control to select the frequency above and below which you want the equalizer to act. Rotating the EQ Gain knob clockwise past its noon position progressively boosts frequencies above the EQ Freq setting while attenuating those frequencies below a commensurate amount.

Rotating the EQ Gain knob counterclockwise from its noon position has the opposite effect, boosting lower frequencies and attenuating higher ones with respect to the EQ Gain setting. For big, pillowy tone on electric bass guitar, set the EQ Freq knob to roughly 100 Hz, and turn the EQ Gain knob counterclockwise from noon.

The SPL Free Ranger graphic equalizer (AAX DSP, AAX Native, AU, AudioSuite, RTAS, VST2, VST3) features four fixed bands respectively centered at 40, 150, 1,800 and 16,000 Hz. Modeling the sound of passive equalizers, Free Ranger sounds particularly flattering on acoustic instruments and full mixes where silvery sweet and round tones are your port of call. Try boosting 40 and 1,600 Hz to add luxuriant weight and open air to the full mix for your ballad, then sign in immediately for EQ-addiction therapy at the nearest clinic.



Fig. 5. PSP’s PianoVerb, a stripped-down version of PianoVerb2, produces unique reverberation using twelve string operators tuned to different notes. When I was a kid, I used to love sticking my head inside an open piano while hammering the keys with the sustain pedal depressed. Now this fascinating sound—absent the childish noodling—is yours for the taking! PSP’s ( PianoVerb (a stripped-down version of the company’s PianoVerb2, available in AAX, AU, VST, and RTAS formats; see Figure 5) produces unique reverberation using twelve string operators tuned to different notes.

Image placeholder title

Controls let you retune, transpose, and detune the string operators and adjust their damping and decay time. For a bright-sounding ’verb, raise the Transpose control moderately and turn the Damping control counter-clockwise to 0%. Discrete discordant tones become audible at very high Transpose settings, transforming acoustic snare and tom tracks into jarring electronic-percussion instruments. Cool!


Fig. 6. Slate Digital’s Virtual Mix Rack (VMR) is yours for the taking at no charge. The virtual effects rack comes pre-loaded with the free Revival Sonic Enhancement Processor and demos of Slate’s compressors, equalizers, and Virtual Console Collection (VCC). The Revival Sonic Enhancement Processor is a module for the Slate Digital Virtual Mix Rack (VMR;, a closed-architecture effects- rack plug-in (AAX, AU, RTAS, VST2, VST3) into which you can load up to eight compatible Slate processing modules (see Figure 6). Revival and the empty VMR rack are both free, while the other modules compatible with the rack—currently including compressors, equalizers, and the company’s Virtual Console Collection (VCC)—must be paid for if you wish to continue to use them beyond their 15-day trial period.

Image placeholder title

Revival has just two controls: Shimmer adds air and brightness to the high-frequency band, while Thickness adds girth to the low end. Goose the Thickness control on kick and bass guitar tracks to fatten them up. Thickness and shimmer both sound terrific on full mixes, but be careful: A little goes an awfully long way in mastering applications.



Fig. 7. Softube’s free Saturation Knob modeled- distortion effect features a three-way switch, labeled Saturation Type, that lets you apply distortion to mostly the lows or highs, or to the entire frequency spectrum. Saturation Knob (AAX, AU, VST) from Softube ( is a modeled-distortion effect that sounds great on a wide variety of tracks, from electric guitars to vocals to trap drums (See Figure 7). A three-way switch, labeled Saturation Type, lets you apply distortion to mostly the lows or highs, or to the entire frequency spectrum. On electric bass, select the Keep High switch setting to preclude adding fizzy high-frequency distortion to the track while enhancing girth in the low end. Conversely, the Keep Low switch setting is your ticket for adding sparkly highs to vocals without inflating bass frequencies. Try using the Neutral setting to add wideband distortion to full-range synth tracks. A solitary knob adjusts how much distortion is added to your track.

Image placeholder title


If you’ve ever been frustrated by overshooting your mark when mouse-dragging your DAW’s teensy-weensy faders, you’ll love the Sonalksis ( FreeG (AU, VST).

Fig. 8. Sonalksis FreeG provides a long-throw fader, peak and RMS meters, pan and trim controls, and switches to invert polarity, mute signal, and bypass. This fantastic plug-in provides a long-throw fader the length of a bowling alley! Joining the fader are peak and RMS meters, pan and trim controls, and switches to invert polarity, mute signal, and bypass the plug-in (see Figure 8). Activate the Pre switch to view signal levels at the plug-in’s input for comparison purposes. When you want to make small, ultra-precise fader adjustments, turn on the Fine function to shrink the fader’s decibel range while preserving the length of its throw. Essential for both mixing individual tracks and use as a master fader, every engineer should own FreeG.

Image placeholder title

Michael Cooper is a recording, mix, mastering and post-production engineer, and a contributing editor for Mix magazine. You can reach Michael at and hear some of his mixes at