Thursday, November 30, 2006

Signal Processors, Equalizers, and feedback Control

Signal processors fall into three main categories based on which property of the audio signal they affect: equalizers affect frequency response, dynamic controllers affect amplitude, and delays affect time properties such as phase. Each of these can be useful in the operation of microphones but the equalizer are of particular interest because of their potential use in feedback control.

Feedback is a very frequency dependent phenomenon because it occurs first at peaks in the overall sound system frequency response. Equalization of the response may significantly affect the onset of feedback. Equalizers are frequency dependent filters that fall into several categories based on the characteristics of the filters and their adjustment. Hi-cut and Lo-cut filters progressively attenuate, or reduce all frequency. That is, the attenuation increases with frequency further above or below the cut off frequency. The cutoff frequency may also be adjustable from a minimum of 6db as to steep as 24db. Hi cut and low cut filters are used to reduce the bandwidth or frequency range of the signal to remove unwanted high frequency or low frequency sounds such as hiss or rumble. Shelving equalizers allow low frequencies to be cut or to be boosted. The cut or boost is not progressive: it is the same as all frequencies below or above the filter frequency. The response curve looks somewhat like a shelf above or below the filter frequency. The amount of cut or boost is adjustable typically up to plus or minus 15db/ the filter frequency is usually fixed: about 250 Hz and blow for the low frequencies, about 8000Hz and above for the high frequencies. Shelving equalizers are used for general response shaping at low or high frequencies. They are the type of filter used as bass or treble tone controls. Bandpass equalizers allow frequencies within a certain band or range to be cut or boosted. They are classified according to their bandwidth and/or according to the number of filters employed. Bandwidth is usually given as a fraction of an octave. For example a midrange tone control is a single bandpass filter with a 1 octave bandwidth designed to affect the frequency range between a bass control and a treble control, typically 500Hx-1000Hx. Again the range of cut or boost is typically up to 15 db. Bandpass filters have fixed frequency and fixed bandwidth.

Thursday, June 29, 2006

Detailed Explanation of How Sound Waves Behave at Places of Worship

There may be terms in this article you are unfamiliar with, or perhaps you may be unclear regarding our use of the term[s] in a specific way. We are pleased to offer an audio glossary so that you may be become better acquainted with the language in this article.)

Certainly not just true of places of worship, excellent sound quality (not just quantity or volume) is the primary goal for purchasers and professional vendors (installers) alike. Because sound quality is important for church sound systems, it is helpful to become familiar with some of the more general aspects of audio or sound. In this article, we will examine in laymen's terms how audio/sound is produced, transmitted, and received by the target or listener (congregation, audience, etc.) and we will describe exactly how the audio/sound wave behaves.


I. How Audio is Produced, Transmitted & Received (Heard)

Sound waves, what we call audio, are produced by vibrations in the wave source, such as vocal chords, percussion instruments, guitar strings, etc. Any easy way to imagine sound waves is seismic waves. Similar to the illustrations we've all seen on news broadcasts, seismic waves travel much like sound waves - from the source of the vibration - to the target where they are felt or heard, as an earthquake or a noise or both as the case may be. In a place of worship, the most common sound sources are musical instruments, loudspeakers, and of course human vocal cords.

When an audio source (in this case let's say a female soloist's vocal chords which produce movement when she forces air through them) produces sound, the mechanical vibrations of the vocal chords move the air which is immediately adjacent to them. This movement continues from her throat to her mouth and out of her mouth ultimately to the microphone, alternately pushing and pulling the surrounding air from its resting state. Each back and forth vibration produces a corresponding pressure increase (compression) and pressure decrease (rarefaction) in the air (hence the sound wave - ebb and flow).

A complete pressure change (wave), or cycle occurs when the air pressure goes from rest to maximum to minimum and back to rest again (from valley to crest to valley in the case of an ocean wave). These cyclical pressure changes travel or radiate outward 360 degrees from the singer's vocal chords, forming a pattern called a sound wave. These sounds waves, transmitted in premium quality by a professionally installed sound system, eventually enter the air space around the ears of a congregation member and interact with the inner ear (tympanic membrane and ear drum) which begin vibrating in unison with the waves, thus allowing the member to "hear" the singer.


II. Acoustic Behavior of a Sound Wave (Audio)

A simple sound wave can be described by its frequency and by its amplitude. The frequency of a sound wave is the rate of which the pressure changes occur (how fast the waves roll in and out in the case of the ocean wave). It is measured in Hertz (1Hz is equal to 1 cycle each second or 60 cycles per minute). The audible range (what we can hear) of frequencies to the human ear extends from a low of about 20Hz to a high of about 20,000 Hz. Animals such as bats, dogs and cats have a much great audible range that humans do explaining why our pets are so much more sensitive to loud radios and television settings than we are. The same phenomenon is true of light - the sun's light travels in a spectrum far greater than human eyes can see unaided (such as ultraviolet, infrared, x-ray, etc.)

If at any point in the transmission process an interruption occurs, the sound quality is diminished - sometimes heard as static, clicks, dead spots or other anomalies in the audio transmission. ProAudioSuppliers.com is experienced in the customization and installation of premier sound packages for places of worship. Our installers work directly for the company and not subcontracted, so we can say with confidence that your new sound system will operate free of interference and quality-disruption for the life of your system, guaranteed.

Monday, May 29, 2006

Sound Systems & Common Audio Challenges for Places of Worship

Places of worship such as churches, tabernacles, auditoriums, synagogues and even gymnasiums require specific types of sound systems for worship services. Standard or pre-packaged sound systems regularly fail to adequately meet the needs of these specialized users due to the types of sounds sources most commonly utilized during services such as the spoken voice, varying acoustic instruments, choral ensembles and even playback devices such as compact discs and pre-recorded musical arrangements.

With regard to the spoken voice, either male or female; we find that the vocal range of the spoken word during a worship service can vary widely from extremely soft, such as during the Invitation or prayer, to extremely loud and carrying, such as a point of emphasis during the minister's sermon or a blessing called out over the top of a hymn on the piano and organ. To further refine the quality of sound in a church or temple, one must also consider the distance between the sound source (in this case a spoken voice) and the piece of equipment used to translate the voice or sound to the congregation (in this case a microphone). When an individual is speaking or singing, the source and the equipment are normally in close proximity but in the case of a choir or play presentation, we may have many voices at varying distances from the microphone equipment to consider. Specific microphones are available for specific types of formats such as wired microphones, wireless microphones, small noise-cancelling mics that attach to lapels or collars and ear mounted mics that for hands-free movement and excellent clarity.

Musical instruments also present similar challenges when installing a proper professional sound system in a place of worship. Ranging from a simple acoustic guitar to a massive pipe organ or even a full orchestra; places of worship present professional sound installers with a sure challenge every time. Pre recorded music is also a very common component in worship services featuring a visiting guest singer or performers. While audience members must be able to hear and enjoy the track's sound, it is most important that the singer or group be able to be heard clearly and in unison with the chosen tracks for maximum impact.

In addition to "desired sound sources" in a place or worship (instruments, voices, etc.), there exist certain "undesired sound sources" that are detractors from your message to varying degrees. Examples of "undesired sound sources" are background noise from the air conditioning and heating systems, buzzing or humming light fixtures, street noise such as passing traffic and emergency response sirens, even fussy babies and children can become quite a problem when attempting to record a quality reproduction of the service. Did you know that even some "desired sounds" can become a problem such as the organ overpowering the choir or the fragile voices of timid children during the Christmas pageant or Passion Play? Ironically, the speakers themselves and the sounds they transmit can become a powerful challenge to plan for when installing church sound systems. Better known as "feedback", the sound system can begin picking up its own transmissions and feeding it back through via the microphones. This sometimes creates the ear-splitting squeaks and squelches that can momentarily interrupt a performance and sometimes destroy the message or moment for the congregation. Only a professional, experienced audio consultant can anticipate and avoid such problems on a basic design level and only proven installers should be trusted to install your equipment per the consultants design (contact our consultants & installers).

In addition to selecting the perfect sound equipment for your budget, your specific place of worship also plays a large role in determining how the equipment will be installed. Better known as "acoustics", size, dimensions and materials in the auditorium greatly impact the way the system will sound once installed and operational. Your auditorium's "acoustic nature" (the environment in which the new sound system will perform) may have a positive or a negative effect on the audio produced by voices, instruments, and loudspeakers even before the sound is picked up by microphones or heard by the congregation; absorbing or diminishing some sounds while reflecting or reinforcing other sounds. Strong reflections can contribute to undesired sound in the form of echo, standing waves, or excessive reverberation. A true professional knows that something as variable as the size and seating preferences of the congregation itself will have an impact on how the speakers and microphones should be placed around the auditorium!

In light of these many variables, it is imperative to choose wisely when selecting an audio professional to outfit your place of worship. ProAudioSuppliers.com caters specifically to places of worship and personally invites these groups to contact us for a consultation, free of charge and obligation; we'd like to offer our experience and expertise. Contact ProAudioSuppliers.com now to schedule a visit.