Radial Engineering Q4 Equalizer

500-series 100% Discrete State-Variable Class-A 4-Band EQ Module

By Phil O'Keefe

Unlike the vintage-inspired Radial Engineering Q3 induction coil equalizer module that I reviewed previously, the Q4 is a modern semi-parametric equalizer design with high and low shelving EQ filters, as well as two semi-parametric midrange bands.

Housed in an all-metal case that provides excellent shielding, the Q4 features the solid, rugged build quality that is one of the hallmarks of equipment manufactured by Radial Engineering - but there's more to it than just solid construction, so let's take a closer look at the details of this 500 series four-band semi parametric equalizer module.

What You Need To Know

• The Q4 is designed for use in 500 series racks. I tested the Q4 in my Radial Engineering SixPack, but it will also work in any other 500 series rack. As with all 500 series modules, the host rack unit provides the physical input and output jacks for the Q4 equalizer, as well as providing power for the unit. The Q4 EQ features balanced I/O and is designed to operate at +4dBu line level.

• The Q4 is a bit different than the semi-parametric equalizers that have come before it. Unlike previous designs, it uses 100% discrete class-A electronics, with no integrated circuits. Discrete electronics take up more physical space, so it can be difficult to get everything into a single 500 series module when using discrete electronics while keeping the routing optimized and the noise levels low, but the sonic benefits make the effort worthwhile, and the noise levels of the Q4 never seemed particularly high to me in my testing. The Q4, while similar in look and function to the four band semi-parametric equalizers found in many mixing consoles, sounds much richer, more detailed and subjectively "better" than the EQ you'll find in all but the most high-end consoles. 

• There are four EQ bands on the Q4, which are labeled High, High Mid, Low Mid, and Low.

• The Q4 features high and low shelving EQ filters. The High EQ knob controls the 10kHz shelving filter. There is 12dB of boost or cut available. The Low EQ knob controls the 100Hz shelving filter. Again, there is 12dB of boost or cut available.

• For manipulating the crucial midrange frequencies, two filters are provided - both of which are semi-parametric, sweepable filters.

• The High Mid band can be swept from 1kHz to 8kHz. Once you've found the frequency you want to adjust, up to 12dB of boost or cut can be applied.

• The Low Mid band can be swept from 300Hz all the way up to 2.4kHz. As you can see from looking at the numbers, there is some overlap between the range of the Low Mid and the High Mid bands, which can come in handy in some situations. As with the other three bands, up to 12dB of boost or cut is available in the Low Mid band.

• There are Q switches on both of the semi parametric midrange bands. These switches have two settings, with a wider bandwidth setting for more broad tonal adjustments, and a narrow bandwidth setting for more precisely targeted adjustments. 

• Are you wondering what the bandwidth is for the two settings on the two bandwidth switches? I suspected that the bandwidth would vary, depending on how you had the other controls set, so I called Radial up and asked them about it. This is what they had to say: "Because the Q4 is a Class-A device, there is no set bandwidth on the Q filter switch; the bandwidth of either Q setting is variable based on boosting or cutting the signal and also where you are positioned within the frequency spectrum of the HI/LO-MID parametric equalizer portion of the Q4.  The narrow Q setting will act as a more surgical tool when you are trying to fix a specific troublesome frequency."

• An EQ In switch allows you to bypass the EQ at will, allowing for direct comparisons between the processed and unprocessed signal. A green LED next to the switch illuminates when the Q4 EQ is active. 

• The Q4 EQ carries a three year transferable warranty.

Limitations

• Unfortunately, there is no gain control on the Radial Q4. If you do extensive cuts, there's no ability to compensate for the signal level loss associated with those cuts. Any make-up gain would have to be provided by subsequent devices in the signal path, or by setting the output level of the device (such as a mic preamp) that is driving the Q4 higher. The same is true for boosting frequencies - excessive boosts can result in clipping of subsequent stages of the signal path, such as your audio interface's inputs. Again, the solution is to either lower the level of whatever is feeding the input of the Q4, or possibly lower the level on a subsequent device in the chain, assuming it has sufficient headroom and wasn't being driven to clipping itself by the hot signal from the Q4. In this respect, the Q4 functions exactly like console-mounted equalizers, which also typically lack separate gain controls.

Conclusions

This looks like a mild-mannered, garden variety four band "board style" semi-parametric equalizer, but it only goes to prove that the old adage is still true - looks can be deceiving. While it isn't a true parametric EQ with fully variable bandwidth control, the addition of the Q switches on the two midrange bands gives it more flexibility than most semi-parametric equalizers, which typically only offer a fixed bandwidth setting. Usually, such designs use wider bandwidth settings that are best suited to tonal shaping as opposed to more surgical and corrective narrow-bandwidth equalizers. The Radial Engineering Q4 gives you that wide bandwidth when you want it, but also the option of the more precise narrow-bandwidth setting when you need to make more narrowly targeted corrections.

The lack of an output gain control is the only minor annoyance, but to be fair, you won't find them on the equalizers included with most mixing consoles either, and there are well-known ways of optimizing the gain staging, even without a make-up gain control, so the lack of one is not going to be a deal-breaker for the vast majority of engineers.  

The sound of this equalizer is what really sets it apart from similarly featured four band semi-parametric EQs. Because of the Class A configuration and discrete topology the sound is warmer and arguably prettier, sweeter, purer and more refined than most equalizers of this type, with that certain je ne sais quoi that sets the really cool gear apart from the rest of the pack. It's the type of unit you buy for utility equalization duties, but that will surprise you with its high quality sound and flexibility. It's another solid performer from Radial Engineering that is well worth checking out if you are in the market for an EQ to use in your 500 series rack. 

Resources

Radial Engineering Q4 ($800.00 MSRP, $599.99 "street")

Radial Engineering's Q4 EQ web page 

Specifications and a block diagram can be found right here