Walrus Audio Mira Compressor Review

In the Spanish language, Mira is a command that translates to look, see, and call attention to. Walrus says, "With the Mira Optical Compressor, you're creating and shaping studio-grade timbre that demands to be seen, heard, and above all, felt."


You can read my earlier review of the Walrus Audio Deep Six compressor which is an OTA circuit and is inspired by the Universal Audio 1176 with the simplicity of the Ross and Dynacomp circuits. As follow-up I reviewed the later Deep Six v3 which featured a Tone control which is essentially a bass roll off. Both of the Deep Six compressors make for a fine choice of compressor pedal. With Mira, Walrus Audio is back for another round with an optical design this this time. Optical circuits use a photocell as a detector and a light bulb to determine the gain reduction. One of the most famous optical compressors is the the LA-2A.

True to form, the Mira offers transparent, buttery smooth, balanced and warm compression.

Mira definitely has an inherently warmer take on compression than the Deep Six.

Like all Walrus Audio products, the packaging is impressive. Mira comes in a cloth sleeve, beautifully designed box, very nice full-color user manual, stickers, and Walrus Audio guitar pick. First class all the way around. There are 7 dials on the face of the pedal and two LEDs and one foot switch to activate the compressor.


The Level dial sets the overall output volume of the pedal. There is plenty of clean gain on hand which I suppose enables the Mira to serve as a device to increase the overall gain of a signal path. You can use the Level dial to increase or decrease your unity volume level.


There is a Blend dial so you can control the amount of compressed signal that is mixed with your original dry signal at the output. With the control all the way counter clockwise, all compressed signal is removed and only your dry signal is present. Conversely, all the way counter clockwise is fully compressed with all dry signal removed. I consider this to be one of the most valuable features of a compressor because it allows you to dial in as much (or little) clarity as you want while benefitting from the value a great compressor offers. Things like added sustain, limiting effect, and balanced tone. Rolling in some dry unaffected signal can help maintain that organic feel while allowing more dynamic nuance to get through. The Make-Up dial sets the amount of gain applied to your signal after it has been compressed. The more compression dialed in, the more make-up gain you will want to add back to counteract the volume level drop. There is plenty of gain on tap, even when dialing it more aggressive compression.


The Threshold dial is used to set the point at which the compressor will start engaging based on the intensity of the signal hitting the circuit. Turning the dial more counterclockwise is a lower threshold meaning more less signal intensity is required to hit the threshold at which the compressor will kick in. Turning the dial more clockwise increases the threshold meaning more intensity will be required before the compressor will start compressing. I recommend starting with the threshold dial around none which will mean much of your signal should trigger the compression engine. Then move on to the Ratio, Attack and Release controls. All of these controls are highly interactive so after you have made adjustments, use the threshold dial to refine at what signal intensity you want the compressor to clamp on.

How much volume reduction occurs after the signal crosses the threshold is controlled by the Ratio dial. The higher the ratio, the more the signal is compressed after crossing the threshold. The range of Mira is about 1:1 - 20:1 which is very subtle to limiting territory. Then use the Attack dial to control the transient signal allowed through once the signal has crossed the threshold. If you want more of the initial transient through, rotate the dial clockwise for a slower attack. Counter clockwise will give you faster attack times. The Release dial allows you to establish the amount of time before the signal goes below the threshold. Counterclockwise is a faster release. Rotating clockwise extends the release time for more sustain. All of these controls work together and you should use your ear, and playing style, to dial on your desired response. Of course there is no right or wrong combination of settings.


Mira does have a gain reduction LED in the center of the face of the pedal which illuminates more intensely as gain reduction is happening and compression is being applied. The brighter it illuminates, the more gain is being reduced. Gain reduction LEDs are quite helpful to communicate visually how the compression engine is responding based on your settings. I much prefer an array of LEDs for this function, but a single LED is still quite useful. With Mira, as soon as power is applied to the pedal, this Gain reduction LED does illuminate a bit even though no signal is applied. I asked Walrus about why it illuminated with no signal and they replied saying,


"The gain reduction LED is calibrated to accurately show the gain reduction that is being applied to the signal. That will put the LED in the spot JUST before it fully illuminates. If it was fully off before it started, then it wouldn't be accurate!"

That said, I found that because of this, using the compressor outdoors or in scenarios where there is bright light and with lighter compression dialed in, it can be somewhat difficult to see changes in the brightness of the LED. At higher compression settings (lower threshold, higher ratio, etc.), there is no issue. The LED is highly responsive.

Mira also includes a push button on the side of the device. When pushed in, a High Pass Filter is introduced. This featured is very effective for bass guitar where you might want less low end frequency (120Hz or below) to trigger the compressor as much. Essentially, this means the compressor will help maintain low end dynamics. With guitar, I'd just leave the switch out for normal operation. With bass guitar, I really like this feature. It's not that there isn't compression taking place, but the lows aren't causing the compression to react too quickly. For a 5 string bass, it doesn't clamp down as much, suppressing that bottomless, airy feel we often want. Compressors like the Empress Bass Compressor offer more control of the High Pass Filter but the simple switch implemented in Mira is very much useful.


I am very much a fan of having full control over the threshold, release, ratio, and attack in a pedal board friendly compressor. In the case of Mira, I'd prefer that the Attack and Release controls be full-size dials. But this is a minor quip.


Mira requires a 9 volt DC center negative power supply and isolated power is recommended. 200ma minimum is required. Aesthetically, it's always nice to see creativity. Your call on whether you like the enclosure art or not. There is a white LED that illuminates when the pedal is activated by the True Bypass foot switch. In and out jacks are top mounted as is the power input.

Inside, there are a couple of surprises in the form of two trim pots. One of the trim pots is used to set the bias voltage that drives the LDR (Light Dependent Resistor) in the circuit. The other trim pot is used to tune the resistive element in the LDR. Both of these are calibrated during the build process and need to be precise in order for the compressor to operate properly. I reached asked Walrus about these trim pots and I was told they would not recommend making adjustments to these trim pots so I did not adjust them or perform any tests with the pots in different positions. How does Mira sound and perform? It is definitely on the warmer side. Words like "transparent", "smooth", "quiet", "versatile" and "organic" come to mind.

Mira isn't some sort of "tone magic" device, nor is it intended to be. It's all about clean, high-quality utilitarian compression — some might say, "studio-grade" tone in a pedalboard friendly box.

I quite like it. It's a wonderful example of what a highly versatile and controllable, quality optical compressor should be. In many ways, it reminds me of the Broughton Omnicomp though the Broughton offering is a bit brighter sounding. Much of how I described the Optocomp is relevant here with Mira too. Both are real solid performers offering the same functionality albeit implemented somewhat differently. Mira gives you control of disabling the high pass filter. Mira includes a Level control though I'm not sure how important this is for most users. Depending on your pedal board chain configuration it could be useful. Mira is real nice compressor. I've said this of other devices but it is especially relevant here. Mira is one of those devices that makes it more enjoyable to play your instrument. It is versatile the sense that it offers comprehensive controls to dial it in and it can be very subtle and transparent or full-on squishy. It's quiet. It's well-built. It sounds great. It's a nice example one of those compressors that you can hear (and feel) pretty quickly what is going on. Did I mention it sounds and plays buttery smooth? Because of the HPF circuit, Mira is a great choice for bass guitar. For this reason, if you are looking for an optical design, Mira could be a great choice.


Mira is all about sweetening your sound, taming your transients and tightening up your tone.

It will work equally well as an always-on compressor or compressor with boost or to engage for specific purposes. It's great with bass and guitar and is the kind of device that I suspect anybody would find useful. Pros: • Smooth, warm, versatile compression • Great always-on compressor • Quality • Highly configurable • Quiet • High Pass Filter is especially useful with bass guitar and low B string • LED gain reduction meter

• Transparent enough to be useful with virtually any instrument

Cons • Maybe too warm for some • Possibly too many controls for some

• Possibly not colorful enough for some • LED metering not nearly as robust as other compressors on the market today (but at least there is one LED). Can be some

what hard to discern level of intensity in brighter light. • Some users might find the small size of the Attack and Release dials difficult to use Retail price: $249 WalrusAudio.com