In its most basic role, a DI converts an unbalanced signal from an instrument (left) to a balanced signal (right) that’s appropriate to send to a mixing console down (possibly) very long lines.
Most musicians own their own instruments with obvious exceptions such as pianos and pipe organs. And most modern musicians own whatever ‘stomp boxes' they wish to use in obtaining their personal signature sound. But who owns the DI's? On one side of the equation the DI can be looked at as a system requirement, much like stage boxes and snakes, the console, the mics, the main PA, the stage monitors, and so on.
On the other side though, is the perception of the DI as a sound shaping tool. While no DI is ever going to make as noticeable of a difference in tonality as a phaser, flanger or equalizer, still, a DI's contribution to sound quality can be significant. While very important in a live application, DI's are especially true for recordings or broadcast work, in which subtle differences in tonal range can make all the difference in the success or failure of the work product.
One idea is that the ministry, which usually has greater resources than individual musicians, might invest in a selection of DI's in the same way that there's usually a selection of microphones in the mic locker. If, after time, some models are not being used regularly, they can be easily sold. DI's tend to hold their value well, as there are few moving or damageable parts.
DI's IN RECORDING AND POST PRODUCTION
Here's an example of creative DI usage: let's assume that the bass player may not have achieved optimum tonality for a given song. Perhaps she was using an effects device, like an automatic wah-wah that sounded good at the time, but now is indelibly inked onto the track, overpowering the tonal range of the other instruments.
Not a problem. If you've captured her bass on a DI directly from the instrument…in addition to mic'ing the amplifier… you can later post-process the ‘straight' DI track to make the bass stand out - or blend in - as needed. For example, I once put an MXR “Distortion +” on the clean recorded track of a Rickenbacker 4001 to give it presence in the mix. Solo'd, the track sounded awful with the MXR in the loop. But in the mix? A whole different story! It sounded great. But that's another topic…
LINE OUT OR SPEAKER OUT?
This question goes to the crux of working with electric instruments. As with many good questions, the appropriate answer depends on what you intend to do next… in this case with the signal. If the goal is to reproduce exactly what the instrumentalist hears on stage over the house PA, then the solution is clear. You'll want to take the DI feed from the amplifier's line level output o its speaker level output. But why choose one over the other? And what are the differences? Simple:
If the tonality of the instrument has been shaped by the front-end of the instrument amplifier (i.e. overdrive, reverb, or other effects) then the amplifier's line output should provide a high quality line level signal that reflects any tonal settings the artist made to the amplifier's tone and effects controls.
If, on the other hand, the amplifier's power stage is intentionally being overdriven to create a certain tonal landscape, then that will be best captured by connecting the DI to the amplifier's speaker level output. It's important to make sure that the DI you're using can accept speaker level. If a given DI does not have a clearly marked “Speaker Level Input” or a -40 dB attenuation switch, it could damage the DI to connect it to an amplifier's speaker output.
Stereo DI's
DI's are available in a myriad of types these days, one of the most useful being the stereo version. If your sound system, your recorded work, or your broadcast will be in stereo, then it makes a lot of sense to take a stereo feed from any keyboards that are present. By combining two high-quality DI channels into one box, the clutter with cables is reduced and any troubleshooting that might be needed just got a lot easier.
Active vs. Passive DI's
Much can be written on this, but it all comes down to how a given DI sounds on a given instrument. But wait! It's not just about sound. The DI is there to eliminate hum, buzz, and other forms of interference. To do so requires that the DI convert an unbalanced signal from an instrument to a balanced signal that's appropriate to send to a mixing console down (possibly) very long lines. The only way to achieve true galvanic isolation, which essentially means eliminating mismatched ground references in the system, is by means of a transformer. Active, balanced output circuits can mimic some of the qualities of transformers, but they cannot interrupt the ground reference that causes hum and buzz in the same way that a transformer can. DI's that use high-quality, precision transformers are expensive because the transformers are manufactured in small quantities and are themselves expensive. And not every worship center needs to drive very long lines or will encounter complex interference problems. The best advice here is to try a variety of DI's to determine which ones will meet the needs of your ministry, without costing more than you can afford.
Exotics
A quick search on any pro audio sales site will reveal that there's a booming business in exotic DI's. Many brands are available and a wide range of prices… from a few hundred dollars to a few thousand dollars…are common. Many, if not most exotic DI's, include one or more channels of mic preamps. Often tubes are used in the circuitry. Is an exotic DI right for your specific situation? It might be, but it's always worth testing any unit that you're considering purchasing, prior to making a commitment.
