Review of the Rolls LiveMix 34c two-channel microphone field mixer (for linguists)
Introduction: About Rolls Corporation and their products
Rolls Corporation is an innovative audio electronics manufacturer specializing in interface accessories, mixers, amplifiers, signal processors and signal sources. To quote information from Rolls website: "Rolls began in 1989 when Marilyn and David O. Di Francesco introduced the HR100 amplifier, the HR11c Microphone Processor, the HR6x mixers, and the HR210 EQ - all half rack at the New York AES Convention. David is well known and respected in the professional audio electronics industry, his first company still bears his initials."
Having used Rolls products for quite some time, I can attest to their quality and durability. Most products have a solid build, based on simple, yet very functional designs. Rolls makes products that are either absent from the competitors' lineups or are not particularly affordable. Linguists will be pleased to find a number of quality headphone amplifiers and mixers in the Rolls inventory.
I have had a really positive experience dealing with Rolls product support staff and I am convinced that they are perfectly capable of providing first-rate warranty and service.
The LiveMix 34c
The MX34c LiveMix is a two-channel microphone mixer. Although having many uses, this little mixer was originally designed with the video camera operator in mind. Many consumer and professional camcorders have either a simple stereo 1/8-inch microphone input (with plug-in power), or a pair of mic/line XLR inputs. Most of them lack any mixing options and onboard phantom power supplies. In order to interface a pair of professional microphones (say, in a typical one-on-one interview), it is best to use a dedicated, stand-alone microphone pre-amplifier/mixer, such as the Sound Devices MixPre, reviewed on this site. You can read more about recording high-quality audio with a video camera in this post.
If you use a small flash-memory recorder, such as the Sony PCMM10 field recorder, the same principles apply. Such recorders typically include a plug-in power stereo microphone input, which works best with dedicated stereo microphones, such as the Sony ECM-DS70P. However, while most plug-in power recorders are capable of really decent recordings, they are virtually useless for serious speech research. Thus, the researcher has to obtain a dedicated microphone pre-amplifier in order to interface a professional speech recording microphone, such as the Audix HT5, with the digital recorder. The LiveMix MX34c is designed to do just that.
Design and specifications
The LiveMix MX34c (Figure 1) is a small (about the size of a VHS tape), all-metal, sturdy device. The build quality appears to be very high, certainly better than most of the flimsy, plastic audio devices available in this price range. The inputs and controls have a dependable feel, are logically laid out, and clearly marked. The are two strap eye holes on the front, which comes in handy if you want to carry the mixer over your shoulder.
Figure 1. The Rolls LiveMix MX34c is built on a small, all-metal chassis.
The front panel (Figure 2) contains gain and pan controls for each microphone input, as well as an independently powered headphone monitoring input (1/8-inch stereo) and a control knob. In addition, there is a small blue LED, which is lit when the unit is powered on and dims when the battery power is low. The knobs have a gain scale in 10 increments, and click in the middle of the scale (top-most position). Each channel has a Level and Pan control, and a separate headphone circuit that allows monitoring signals without effecting the main output signal.
Figure 2. The Rolls LiveMix MX34c front panel
The rear panel (Figure 3) contains two XLR microphone inputs and a stereo 1/8" (3.5mm) output. The 3.5mm output may be switched to either a mic or line level. There is also a stereo 1/8" (3.5mm) auxiliary input for connectiing to any stereo line-level source such as an AM/FM tuner, CD player etc. The power switch, mic/line toggle, and a 12 V AC adapter input complete the rear panel. Because of the close proximity of the mix/line selector to the stereo output, you will need to use slim-profile 1/8 connectors (angled connectors probably won't fit), but it is a minor inconvenience.
Figure 3. The Rolls LiveMix MX34c rear panel
On the left side of the mixer, you will see phantom power DIP switches (see the close-up imaged embedded in Figure 4). Unlike the vast majority of inexpensive field mixers and recorders, the LiveMix offers independent powering of each microphone input, thus allowing mixing microphones that do and do not require phantom power. I consider it a major advantage. For example, while interviewing subjects in the field, I like to use my Sennheiser HMD 25 headset microphone for myself, and a condenser microphone for the subject. The Rolls LiveMix allows me to selectively power only the condenser microphone.
Figure 4. A close-up image of the phantom power DIP switches
On the right side of the mixer, you will find two 9 V battery bays (Figure 5). It's a very well-designed battery compartment allowing quick and easy battery changes. The LiveMix takes two 9 volt alkaline batteries, which ensures adequate power levels for most condenser microphones.
Figure 5. The 9 V battery bays
Of course, the solid and functional design is only secondary to actual acoustic performance. For most speech and hearing research applications, we do not care so much for the subjective sound quality but we absolutely do care about a flat frequency response and a relatively high and clean gain. In other words, is there any benefit to using the LiveMix instead of just making do with most field recorders' out-of-the-box audio performance?
Having tested the unit with a number of different microphones, I have concluded that the LiveMix is perfectly capable of providing the missing interface to many of the popular solid-state field recorders. There is more than adequate gain and a relatively low inherent noise. With medium-sensitivity condenser microphones, in order to obtain adequate recording levels of conversational speech, you will probably have to set the gain of your field recorder (line-in) and the LiveMix to about 50% of their gain range. Note, that the line-in setting on your recorder is much quieter than your mic-in setting. Therefore, you end up with ample microphone gain and a respectably low noise.
On-board phantom power adds just a bit more noise, which is expected of a device in this price range. I often recommend using self-powered microphones not only to save your recorder's battery life, but also to help avoid the extra noise generated by your recorder's phantom power supply. Figure 6 shows comparison spectra of self-noise between the settings with phantom power on off (left panel) and on (right panel). The increase in noise is moderate, and it should not significantly influence the quality of your recordings.
Figure 6. A comparison of FFT spectra with phantom power turned off (left panel) and turned on (right panel)
The Rolls LiveMix MX34c turns out a surprisingly good performance with dynamic microphones. Figure 7 shows a spectrum of self-noise generated by a recording chain consisting of the Sennheiser HMD 25 dynamic microphone, the LiveMix, and the Fostex FR-2LE recorder (via the line-in interface). The gain was set to about 75% of the maximum range on both the mixer and the recorder, which ensured ample gain with a reasonably, and somewhat unexpectedly, low noise.
Figure 7. A spectrum of self-noise generated by a recording chain consisting of the Sennheiser HMD 25 dynamic microphone, the LiveMix, and the Fostex FR-2LE recorder (via line-in)
If you need a two-channel microphone pre-amplifier and mixer for your small digital recorder (e.g., Sony PCMM10) at a very affordable price, the Rolls LiveMix MX34c is the only option currently available in the US. The unit is very sturdy and offers a really decent performance. I am very pleased with the LiveMix and I am honestly amazed that so much functionality and such good performance can be purchased for around $100. Once again, Rolls does not disappoint.
Compared to the much more expensive Sound Devices MixPre (reviewed here), the Rolls LiveMix unit does not have LED level monitoring, a high-pass filter, a limiter, or a calibrating tone. None of these features are essential for linguistic fieldwork. They are handy, yes, but you can do without them. In some ways, the MixPre is the ideal two-channel field mixer. The Rolls LiveMix has some catching up to do, but at this price ($100), it would be unreasonable to expect that it would.
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