Some modern digital consoles, like the StudioLive® Series III mixers, provide the ability to delay the input signal at the source. While this feature is extremely powerful, it is often misused or misunderstood. This chapter will explain how to get the most out of an input delay.
An input delay has many uses. On small stages where the guitar amp and the kick and snare mics can be clearly heard in the vocal mic, an input delay can “move up” the backline. Delaying the backline so that the close mic’d signals and the bleed in the vocal mic align with one another at the mixer will decrease comb filtering that blurs the mix. This will tighten the overall mix and give it more clarity and punch.
In large venues, the bottom snare mic can be aligned with the top mic, or the bass cabinet mic can be aligned with the direct line to create a more coherent signal. This is especially useful to prevent phasing problems.
Aligning the Backline with the Vocal Mic
In this example, we will delay the guitar amp’s close mic to match its arrival at the vocal mic. In general, snare drums and guitar amps are the most common causes of backline bleed. Depending on where your vocalist is standing, one or both may need to be delayed to compensate for comb filtering.
- Solo the guitar and vocal channels; notice that all other channels are muted.
- Measure the distance from the guitar cabinet to the vocal mic. Sound travels at a rate of 1,130 feet per second. This means you need to set 1.1 ms of delay for every foot of distance. For our example, let’s say the guitar amp is 5 feet from the vocal mic.
- Using your mixer's input delay option, delay the guitar channel by 5.5 ms.
- Ask your guitarist to play a staccato pulse and listen for any remaining flamming. Move up or down 0.1 ms until you hear the tightest sound.
Aligning Direct and Mic’d Signals
When combining a direct input signal with a mic’d signal from a single source, the direct sound will arrive earlier than the microphone’s signal because the latter’s source has to travel some distance through the air before reaching the microphone. This results in the two signals being out of phase with respect to each other. This problem can sometimes be corrected by alternatively flipping polarity on the direct and microphone channels to find which combination of the two signals provides the desired result. However, by using input delay it is possible to achieve a closer, more accurate phase relationship.
- To begin, solo both the Direct Input channel and the Microphone channel.
- Set the pan position of both channels to the center. This will sum both signals mono and allow you to better hear the phase differences between the channels.
- Increase the delay time on the Direct Input channel. This is the easiest way to hear the change in phase between the two signals. Listen to both till you find a happy medium between the combined signals.
The final result may not be perfectly in time but this is not necessarily your goal. Adjusting the phase relationship between the direct and mic’d signals can help to create space in a mix and keep the sounds coherent.