Tuesday, 22 February 2011

What is a Sound Check?

What is the purpose of the sound check and why does it take so long? This is perhaps one of the most misunderstood - but absolutely necessary - tasks that must be carried out for a special event to run without technical glitches, especially one with a large audience and complicated audio requirements. Event producers must understand that sufficient time has to be allotted to accomplish it. One to two hours - or more - are not unusual for a complete check.

A thorough sound check is done for several reasons.

  • Testing the system. Because of the number of components in most audio systems, initial testing must be done slowly and in the right order so no damage is done to components, mainly speakers. Before the system is turned on at all, the crossover points (i.e. specific frequencies) must be set for all the speakers so that signal power is not too great for the speakers. After this, the system components are turned on in the general order of: effects, EQ, mixer, and amplifiers. This is done with all volume and gain controls (knob that controls the small electrical signal entering the main mixer on each channel) set to zero and most other knobs at a neutral position on the mixer. Following this, the individual speakers (mid/high frequency speakers then low frequency speakers or "bass bins") are tested to ensure that only the correct frequencies are coming through them.
  • Setting equalization (EQ). The main reasons for using equalization (specific frequency adjustment) in an audio system are to prevent feedback and to help create a desired sound. Of these, feedback is of the most concern and the one annoying problem that can keep cropping up throughout an event if this procedure is not done properly. The procedure is done in exactly the same way for main speakers and for monitors. The preferred method now is to use an analyzer system that compares the output of the console with what is heard coming out the main speakers via calibrated microphones in the audience. After going to all this trouble, there may still be a problem with feedback due to the different acoustics in the venue once all the event attendees are present, so EQ usually needs to be monitored continuously during the event.
  • Adjusting individual channel signals. From this point on during the sound check, the band or performers should be present so they can provide information to the audio engineer as to the acceptability of their sound. For this exercise, individual channel signal inputs are tested separately. For example, the lead vocalist’s microphone is tested by first turning the gain control on that channel up until clipping or signal cutoff is shown by a light on the mixer channel. The gain is then turned down just below this level and remains there with no further adjustment during the event. From then on, the only adjustment is to the individual channel faders. The purpose of doing this is to get the maximum possible clear signal from each input source. Once this is accomplished for all channels, then the main mixer faders can be turned up and the individual channel faders adjusted to obtain a suitable overall mix coming out of the main speakers. Most audio engineers will assign a name to each channel at this time on a piece of tape and sometimes will set a preliminary level indication as well for each channel. This entire process can take quite a long time with a large band, so that time must be built into the event schedule. Here is a summary of the relationship amongst the different volume controls on the mixer:
    • The gain control adjusts individual signals as they come into the mixer (i.e. individual microphones or insturment signals).
    • The channel fader adjusts the signal level as it leaves the individual channel on its way to the main fader.
    • The main fader adjusts the entire level of all signals as they leave the mixer on their way to the amps and main speakers.
  • Setting monitor mixes. This is a procedure that in theory is very simple. The musicians onstage decide who wants to hear which of the other performers (either instruments or vocals or both) and then those specific channels are combined in the monitor mixer to create a specific mix that is sent to that person’s individual monitor. If there are only one or two mixes required as with a small band, then this mix procedure can be handled by the main mixer using the auxiliary send channels. If there are too many mixes for the main mixer, then a separate monitor mixer must be set up beside the stage and an audio technician assigned to mix the monitors full-time during the event. Of course, every musical group has different requirements so there is no set mix that can be described. What should be remembered, however, is that although the procedure is simple in theory, in practice it can be the most time-consuming part of the sound check. Event producers should keep this in mind. In the case of musical groups, Tim Lewis of Proshow Audiovisual-Broadcast in Vancouver, Canada, states how important it is to have a band that is organized for the sound check and especially for setting mixes. He cites one group that uses a method of going through the monitor mix procedure one musician at a time by having that musician play while all others raise their hands until their individual mix is perfect. This saves considerable time overall and is one of the best ways to accomplish the procedure if in-ear monitors are used.
  • Setting up effects. This is usually the last part of the sound check and is done to enhance or improve overall sound quality rather than to cover up mistakes or poor musicianship. Effects include reverb (simulates acoustic effect of a large room), chorus (simulates effect of more than one person singing), flanging (makes the sound appear to "whoosh" or pulsate), and are added at this time. The procedure is really just a balancing act in obtaining a nice sound using a combination of the individual channel effects send knob and the master effects send knob (both on the main mixer), plus the effects mixture controls and the effects level knob (both on the individual effect units).
Now that the sound check is complete, it’s time to open the doors and start the event (after crew dinner break, of course)!

Monday, 7 February 2011

Let's Talk Audio Systems

One important technical component of special events that is very misunderstood or, more accurately, not understood at all by a large majority of event planners and managers is the audio system. Why is this important? Well, think of yourself as a doctor. How can you successfully know how to treat people if you do not understand how all the components of the human body work? How, then, as an event planner, can you give your client the best event experience without understanding how the various components of the event work?

I'm going to use the next couple of blogs to review what happens to sound from its origin onstage to the final audible sound that emerges from the house speakers and is heard by the audience. For the purpose of the exercise, let's assume we are working with a nine-piece show band on a large stage in a hotel or conference center ballroom.

Here is what a typical stage plot for the band might look like when they (the band) give it to the event manager who forwards it to the audio company.

With the stage plot in hand, the audio company figures out what equipment they need to successfully make the band sound great. They then set up the room for this and the end result will be something like the following diagram of audio equipment locations in the room (not to scale).

As you can see, there are quite a few extra pieces of equipment which have been added to what started as a simple request from the band. Let's look at what these are, but more importantly, why they are needed to convert the band's sound to one that can be heard by the entire audience. We'll do it by following what we call the audio signal.

First of all, the audio signal begins as a sound wave within the INPUT GROUP of equipment, most of which is generally found onstage. This group of equipment includes vocal and instrument microphones, which convert sound waves like a vocalist's voice into tiny electrical signals. Other members of this group include instrument DIs (direct input boxes), keyboard mixers, and occasionally CD/DVD players controlled by performers.

Second, the audio signal (now comprised of small electrical signals) goes into a transformer-isolated "snake" that sends one set of the same signals to the main mixer, and one set to the monitor mixer. The snake is really just a long "extension cord" that connects all the signals onstage to the equipment the audio engineer uses at the audio control position at Front-Of-House (FOH), usually at least 30 ft across the room. It also connects the onstage signals with the monitor engineer position near the stage. He/she is the person who controls the sound the musicians use to hear themselves because they cannot hear the main room speakers onstage since they (the musicians) are physically behind the main speakers.

Third, the audio signal is processed in the SIGNAL PROCESSING AND ROUTING GROUP, by the main house (FOH) mixer, located at that position typically 30 ft or more across the room from the stage, where it is raised in strength, and has various effects like reverb added in the house effects racks, then is looped back to the main mixer.

Fourth and last, the audio signal goes from the main mixer into the OUTPUT GROUPin which a house equalizer adjusts frequencies, a house limiter controls the maximum strength of the signal, house crossovers split it into different frequency bands, power amplifiers boost its strength, and finally the house speakers which convert it back into sound waves that the audience hears.

That's a very brief and simple overview and no doubt some of the terminology is still confusing although you have probably heard the terms before. In my next post, I will review what is entailed in a sound check and what the audio engineer does during an event, as well as trying to explain in a little more detail what the purpose of all this equipment is.