One of the more serious issues facing engineers who travel without production is consistency of audio quality — or lack thereof. When your entire audio chain is different every night, it’s tough to maintain a high standard of sound, and that’s not taking into consideration the drastic variations in acoustics from venue to venue. In an ideal world we’d all be able to use our preferred gear every night, but the reality is that when you’re relying upon promoter-provided production, it’s “sometimes peanuts, sometimes shells.”
Even if you can’t pack your favorite 48-input desk into a carry-on bag, you can carry (or check as baggage) a small rack with a single high-quality channel designated for your star performer. A huge selection of “vocal channels” is offered from a wide variety of manufacturers. Live sound engineers can thank the recording guys for this, since it’s become the norm for most studios to have a few premium channels for tracking, whether or not they can afford a megabuck mixing console.
» What’s In The Box?
The most critical part of the signal chain after the microphone is the preamp. If you do some math, you realize that compromises have to be made in the production of any mixing console. If we were to budget $500 per mic preamp, your average 32-channel mixing desk would start at $16,000 — not unreasonable, but that doesn’t allow for circuitry and components such as EQ, inserts, aux sends, summing amps, meters, power supplies and luxuries like faders, knobs, video screens or even a padded armrest. Therefore, it becomes apparent that only a limited amount of resources can be dedicated to the preamps. A vocal channel is a more cost-effective way of getting a premium mic preamp for a critical instrument — plus, you can take it with you. Don’t underestimate the power of a good mic preamp. You might be shocked at what you hear from even the most pedestrian vocal mic when it’s connected to a high quality pre.
A basic vocal channel gives you at least two critical audio devices: microphone preamp and EQ, preferably with a high-pass filter (which we’d consider a necessity). Many also include a compressor, and as you examine offerings in the category, you’ll find units that add features such as a de-esser, limiter, expander, low-pass filtering and (in a few cases) variable input impedance. The usefulness of these features will depend upon your application and the microphone(s) you plan to use. One advantage of using an outboard channel is that you are not stuck with the circuit topology of the mixing desk. For example, the Vintech X73 and X81 feature discrete, solid-state Class-A circuitry, while others like the Avalon VT-737 and Universal Audio LA-610 Mk II employ tube circuitry for completely different sonic characteristics — none of which you are likely to find onboard a mixing console. Other popular channels include the Focusrite ISA430 MkII, which features variable input impedance for matching the input to your microphone and (for those on a more modest budget) the PreSonus Eureka, which employs a “Saturate” control for emulating the sound of analog tape. The TC•Helicon VoiceWorksPlus boasts voice modeling as well as modulation and harmony effects.
Typically, output from the vocal channel is patched to the line input of a channel on the mixing desk, bypassing the mic pre — which is often the weak link on inexpensive (and sometimes, even expensive) mixers. You may be able to bypass even more of the console’s channel circuitry by using the channel insert return instead of the line input. Desks that provide separate jacks for insert send and insert return make this easy: simply use the insert return jack as a line input. Consoles using a single TRS insert with tip = send, ring = return (or vice-versa) will require fabrication of a cable that leaves the send contact on the TRS disconnected. That being the case, keep the cable short: TRS send/return insert jacks are by nature unbalanced.
» Where’s the Rack, Jack?
When using an outboard channel you’ll have to plan the physical location of the device. On the surface, this looks simple: put it at front of house where you can see and control it, and patch the snake line into the mic input. If you have a monitor engineer running a separate desk, they may beg to differ. Placing the vocal channel at FOH leaves the monitor mix(er) out in the cold, unable to reap the benefits of the improved signal path.
Locating the vocal channel onstage before the mic splitter affords the monitor and front of house desks the better signal path — and in fact requires a shorter cable run from the mic to the preamp, which is always a good thing. But several issues crop up:
1. Gain control of the vocal channel is now strictly in the hands of the monitor engineer. This can present difficulty in situations where the FOH desk and the monitor desk are very different (e.g., one is a modern digital desk and the other is a vintage analog desk). Perhaps one desk has less headroom than the other and requires a lower signal level from the output of the vocal channel.
2. Compression and EQ requirements for the monitor mix may be drastically different from what the FOH engineer desires — especially when the band is using in-ears.
3. Unless the vocal channel has multiple outputs, the mic splitter will now be operating at line level. Transformer-isolated splitters in particular may not have the headroom to do so without adding distortion.
» What’s For Lunch?
Engineers who have a higher budget, or who are seeking gear that can perform double-duty in the studio might consider traveling with a portable enclosure that houses modules in API’s 500-series format, such as the API Lunchbox or the Workhorse-SixPack from Radial Engineering. The 500-series format provides tremendous flexibility because you can pick and choose the modules you want load into it. For example, you could configure a custom signal path consisting of a Vintech 573 Class A mic pre, an API 550a EQ and a Crane Song Falcon (tube-based) compressor — a combination that’s impossible to achieve in any other manner. Whichever approach you choose, you might be surprised at just how good even a run-of-the-mill microphone can sound when coupled to a quality channel.
The Digital Channel
Some vocal channels, such as the Focusrite ISA 430 Mk II, offer built-in or optional expansion for onboard A/D conversion with a digital output. If you are running a digital desk, you may be able to take advantage of this, but be aware that you’ll have to somehow synchronize the word clocks of the two units or you’ll get audible pops and clicks. If the desk has a word clock output and the channel has a word clock input, you can connect a cable between them (probably a BNC-to-BNC). Set the desk’s clock to “internal,” the channel’s clock to “external” and the channel will slave to the desk’s clock. In addition to the word clock connection, you’ll still need to make a digital audio connection. If the channel provides only a word clock output, you can do this in the opposite direction, or possibly set the desk to sync to the clock that is sent along with standard S/PDIF or AES/EBU digital audio output.
