Review: Line Audio CM4

This Swedish-made small diaphragm condenser mic is a mini marvel that offers far grander results than its proportions suggest.

Line Audio CM4
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Review Overview

Our rating


Our verdict

Superb audio quality with a flat frequency response
Strong off-axis performance
Incredibly reasonable price
Small - can be placed in tight spaces and less conspicuous for live sessions
Respectable levels of self-noise

Lack of pad and wide polar pattern may not appeal to some
Frequency response might be too flat for those who expect instant results when placing a mic

If the wider-than-normal polar pattern suits your way of working, we’d recommend these neat little mics without reservation. They sound great on almost anything but shine in stereo applications.

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Price £159 each
Contact Pinknoise Systems | Line Audio

At MusicTech there is occasionally a product that really catches our attention through frenzied discussion on well-known recording gear forums. The CM4 is one such product, and despite early supply shortages, we’ve finally been able to get our hands on a pair for testing.

For those unacquainted, Line Audio is a (virtually) one-person operation based in Sweden that has chosen to forgo the usual expensive and gimmicky marketing ploys to offer excellent equipment at incredibly reasonable prices. As the outfit’s name suggests, linearity of response in all the gear they make is an obsession. Line Audio has already gained a reputation in the classical/location recording scene with their earlier CM3 microphone, miniature OM1 omni and accompanying preamps. The CM4 is the logical successor to the CM3, with a new capsule sourced from Japan.

The CM3 has a slightly wider polar pattern than some other SDCs – though not as wide as the CM3 – and has been designed with a remarkably flat frequency response, respectable levels of self-noise, plus a neutral off-axis response. This final, and oft-neglected attribute avoids spill sounding coloured in an unpleasant way. That’s important because it’s a common issue with mics at a lower price point. As with the CM3, the CM4 is designed to compete with mics many times more expensive. In fact, several shoot-outs pitch the CM3 against Schoeps’ highly-regarded MK series capsules and have surprised listeners.

Line Audio CM4

Small packages

The mics are compactly presented alongside a mic clip and foam windshield in a no-frills plastic case. Line Audio proudly displays the mic’s specifications on a label on the bottom of the box.

We weren’t fully prepared for how small the CM4 would be. It’s tiny, measuring a mere 7.7cm in length, but smartly finished in black, with machine-drilled holes and ports at the capsule end – so no delicate parts to worry about in a session. There are no switches or other controls on the mic’s body. There’s no high-pass filter, and for loud sources, you may need to use sensitivity pads on your interface or mixer.

The compact form is a real winner for inconspicuous placement during location recording, or tucking into tight spaces, especially around a drum kit.

Stiff competition?

In a simple head-to-head test, we put the CM4s up against a popular, similarly priced small-diaphragm condenser (the Rode NT5) and another costing two or three times as much (the Shure KSM141). For testing, the KSM141 is set to cardioid with filters and pads turned off.

On drum overhead duty in a small recital hall, the NT5s gives a crisp, fairly brittle reproduction of the kit. The NT5s also appear to suffer from the proximity effect with low frequencies thinning out even a few feet away from the sound source.

The pair of CM4s, by comparison, are rich and smooth, with a great bottom end that reinforces toms and kicks without any close mics present. The CM4’s slightly less directional polar pattern means capturing more of the room and slightly less of the stick attack transients; the overall effect is a noticeably reduced dynamic range in the recorded signal compared to the other two pairs. This is helpful on room mics and close-mic’ing an instrument with a harsh attack you want to tame. The Shure KSMs sound full, focused and crisp, with plenty of sharp transients and fizz from the snare. It’s a more pleasing sound than the Line Audio in some respects, but requires more compression in post to even it out. Both the Line Audio and Shure mics require a little more gain than the Rode, too.

While not an everyday application for a small condenser, we next tested each mic on an electric guitar cab. Similar to before, the Rode gave a more strident mid/high range – not at all out of place on this particular sound source – whilst the other two mics were more rounded in tone, with the Shure being slightly brighter again.

On acoustic guitar, a comparison of the three mics revealed a far closer result. Lacking a typical high-frequency presence peak built into its frequency response, the CM4 gave a smoother sound that would probably require a little EQ to help the instrument cut through the mix.

While this may not be as compelling a sound for this application, we prefer linearity to having frequency response peaks. Presence boosts may work well immediately on some sources, but can prove challenging to smooth out in applications requiring a more transparent approach to capture.

Capable all-rounder?

To test the limits of Line Audio’s mics, we recorded all parts of acoustic demo song using only the CM4. This included multiple mandolas in ORTF stereo, accordions, fiddle and even a female lead vocal. Isolated clips for the mandolas and voice are available below, processed only with high-pass filtering to avoid boom. The full mix with EQ, reverb and compression/limiting is also below.

The mic shone on everything we pointed it at, with little effort on our part. Mandolas and fiddle were rounded but detailed, without unnecessary peaks built into the sound that may have otherwise rendered them harsh. With a pop shield installed to avoid unwanted blasts of air (mics like this are very susceptible), the resulting lead vocal line is velvety and natural, really suiting the intended unfussy, live feel of the song. Frequently, small-diaphragm condensers have high-frequency lifts that make them too airy for vocals or too smooth a high mid response that they lack clarity in the vocal consonants. This is not the case with the CM4, and we’d happily audition this mic alongside our go-to large-diaphragm condensers for this kind of lead vocal.

Each instrument sounded natural on mic when recording, requiring only minor EQ tweaks at the mixing stage to allow the parts to slot together (e.g. high-pass filtering plus a timid high-shelving cut or boost).

We’re also pleased to say that the off-axis response is equally impressive. Instruments played even 180 degrees off-axis are scooped in the mid-range, but don’t sound excessively unnatural or uncomfortably resonant. Moreover, when we recorded multiple tracks with the CM4, they blend easily, and the result is rather special.

We believe you’d have to pay a lot more for an alternative mic to match the quality of the Line Audio CM4, even though there are the advantages of pads and filter switches with some of these rivals. With its linear response, versatility and stellar off-axis performance, the CM4 rivals mics by Schoeps and DPA that cost ten times the price. It’s no wonder stock is scarce. You will, therefore, not be surprised to hear that we will be buying a pair for use in future reviews and production!

Line Audio CM4
The CM4 next to a Rode NT5 for size comparison.

Key Features

  • Small-diaphragm electret condenser
  • Wide cardioid polar pattern
  • Works with 24-48V phantom power
  • Comes with a plastic carry case, mic clip and foam windscreen
  • 140dB max SPL (at 48V)
  • 16dB(A) self-noise level
  • Dimensions: 77mm x 20mm / 3″ x 0.78″

Thanks to: Mark Davis for the drumming and electric guitar, and Erin Brown for fiddles and vocals. The song is Rocks of Bawn (trad.), arranged and performed by Erin Brown & Barry Watson.


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