 |
|
|
|
|
|
|
|
 |
 |
 |
 |
 |
 |
 |
|
Jump directly
to an Avlex family brand:
Sitemap
 Frequently Asked Questions:1) Why Do Wireless Receivers Not Need A Volume Control? 2) What Is "Pilotone & Noise Lock" Squelch Control? 3) How Can Signal Dropouts And Noises In A Wireless System Be Prevented? 4) What Are the Differences Between "Antenna-Diversity" And "True-Diversity?" 5) How Can Interference Be Avoided from Karaoke Machines and DVD Players? 6) Why Is a PLL-Synthesized Design Better? 7) Is It Better To Have More Switchable Channels In A PLL Receiver? 8) What Is the "ACT" Function in MIPRO ACT Wireless Systems? (2004.3) 9) What Are the Advantages of Using the UHF Band? 10) The Merits and Applications of Condenser Microphone (2004.4)
Why Do Wireless Receivers Not Need A Volume Control? Back to Top 1. The Pitfalls of Having a Volume Control: Conventional wireless microphone receivers are equipped with a volume control on the control panel for adjusting the output volume, just like a radio receiver. However, a wireless microphone receiver is much more complex to properly adjust than a radio. If not set up carefully according to the recommendations in the user’s guide, it can easily put out a distorted or weak signal and appear to be not operating properly. The fault appears to be in the equipment when it is actually operator-error that is causing the problem. 2. The Ideal System for Optimum Wireless Reception: Mixers and amplifiers have both “LINE IN” and “MIC IN” input jacks. The “LINE IN” input jacks are used for connecting radio tuners, cassette recorder/players, CD players, etc. to the system while “MIC IN” inputs are used for all microphones. The input characteristics of the “MIC IN” jacks are designed and based on the dynamic microphone’s sensitivity and dynamic range. Connecting a microphone to this input will enable you to obtain the optimal acoustic performance by simply adjusting the volume control on the mixer without having to worry about making the proper adjustment of a volume control on the microphone itself as well. 3. The Advantages of MIPRO's Adjustment-Free Wireless Microphone System: A MIPRO wireless receiver’s output level is precisely pre-adjusted during production to match the sensitivity of the microphone capsule, eliminating the need for any further volume control adjustment. Simply plug the receiver audio output cable into the “MIC IN” jack on the mixer and the wireless system immediately delivers optimal sensitivity and dynamic range, thereby avoiding operator-error, accidental actions and erratic volume controls.
What Is "Pilotone & Noise Lock" Squelch Control? Back to Top “Pilotone & NoiseLock” is MIPRO’s original squelch control circuitry, designed specifically to prevent outside interference from affecting the receiver and causing unwanted noise in the wireless system. These two squelch control circuits, used in conjunction with the squelch gain control, can effectively prevent noises from a wide variety of electronic sources. The “Pilotone” system adds a fixed modulation signal to the microphone’s transmitting signal. A “Pilotone” authenticating circuit in the receiver ensures that its output circuit is activated only when a “Pilotone” encrypted signal is received. Signal that is not “Pilotone” encrypted will not activate the output circuit, even if the operating carrier frequency matches. The “NoiseLock” circuit is designed to recognize sudden outside interference signals and prevent the irritating loud noises caused by such interference from coming through the sound system. Momentarily, a loud noise from this interference may come through the system, but the “NoiseLock” circuit quickly mutes the receiver’s output circuit until the interference disappears when it will automatically reactivate the system. The Theory of Pilotone Control Circuitry Design:
The Theory of NoiseLock Control Circuitry Design: After signals are received by the antennas, the signal voltage is demodulated and sent out via the detection circuitry to the NoiseLock Control Circuitry which determines whether the signal is a true audio signal or a signal caused by outside interference. If it is an audio signal from a microphone, the Audio Frequency Output Switch will be opened and permit the output of audio frequency signals. If it is a noise caused by outside interference, the Audio Frequency Output Switch will be closed and no audio frequency signals are permitted to pass.
How Can Signal Dropouts And Noises In A Wireless System Be Prevented? Back to Top 1. What Causes Signal Dropout and “Noise?” When antennas receive signals, they receive not only direct signals from a transmitter, but also other indirect signals reflected from the surrounding environment. Unfortunately, as a transmitter is moved around, these signals may go out of phase which can adversely affect the signal strength. When the signal strength on the antenna falls below the squelch level threshold of the receiver, then the phenomena of "Receiving Dead Point" occurs. When the signal strength is closer to the squelch level threshold, the S/N ratio is seriously affected and the receiver may put out noise instead of a clear audio signal. 2. How Does “True-Diversity” Improve Signal Dropout? A “true-diversity” receiver uses two identical tuners, each coupled to an antenna. Built-in circuitry automatically selects the strongest signal coming from the two tuners so that even if one tuner has a momentary signal dropout, the other will still carry the signal from the transmitter. Under adverse conditions of long distances and weak signal reception, the “true-diversity” receiver will have 5 times fewer dropouts than a non-diversity receiver. If the signal strength increases by 10 dB (3 times), chances of signal dropouts improve to 45 times less than the non-diversity receiver. In short distance operation, there is virtually no dropout, no matter where the transmitter is moved relative to the receiver. Not only does a “true-diversity” receiver give added sensitivity for greater range with fewer chances of signal dropout, but it also has a better S/N ratio when the signal strength is weakened to the squelch threshold level. 3. To Ensure Perfect and Professional Sound Quality, the "True-Diversity" Receiver Is the Best Choice!
What Are the Differences Between "Antenna-Diversity" And "True-Diversity?" Back to Top
"Antenna-Diversity" (or Predictive-Diversity) receiver has two separate antennas installed at different positions coupled to a single tuner via a specially designed CPU. After demodulation, the tuner will generate a control voltage to feed the CPU, enabling it to quickly select the antenna receiving the strongest signal. By having the flexibility to switch antennas, the receiver is thus able to prevent many instances of signal dropout or unstable signal reception. The “True-Diversity” receiver uses two identical tuners coupled with individual antennas mounted at different positions to receive signals from one transmitter. The demodulated signals from the two tuners are individually connected to a special comparator and switching circuit to compare signal strength from both antennas simultaneously, instantly selecting the stronger signal. This gives more continuous signal reception and fewer signal dropouts, especially under conditions of long-range operation or weak signal strength.
The “Antenna Diversity” design is more economical, but because of its single-tuner design, it is not capable of performing an instant comparison and switching to the antenna with the stronger signal. Therefore, its performance cannot match that of a “True-Diversity”system, especially under adverse operating conditions. A truly professional wireless system operator should consider using only a “True-Diversity” receiver for maximum performance capability and dependability.
How Can Interference From Outside Sources Be Avoided? Back to Top 1. Why Wireless Microphone Systems Are Vulnerable to Noise Interference: Unwanted noises can occur unpredictably in any wireless application, with the EMI (Electro-Magnetic Interference) emissions of most karaoke machines and many DVD players being some of the most notorious offenders due to poor shielding. Unfortunately, if the wireless system is not set up properly or is of the wrong type, it may be even more susceptible to these EMI emissions. Many of these problems can be controlled with the squelch control on the receiver. Generally, the squelch control is set fairly low to increase sensitivity and operating range. The illustrations below show the audio spectrums of (Fig. 1.a) the wireless microphone signal only, (Fig. 1.b) the wireless microphone together with the DVD player (turned on), and (Fig. 2) squelch control adjustments.
Generally, the squelch control of the receiver is set up at a lower level to increase its sensitivity and operating range. If the squelch level is set low, there is no signal dropout but the system is more vulnerable to outside interference. Therefore, if noise strength is above the setup squelch level (see red line <SQ1> in Fig. 2), a noise signal will activate the receiver output and a sudden loud noise will be heard. In contrast, if the squelch level is set higher than noise strength (see blue line <SQ2> in Fig. 2), the noise signal will not activate the receiver output and a loud noise will not be heard. However, the receiver's sensitivity will be lowered and any microphone signal that is below noise strength will not be received. The operating range will also be decreased with the higher squelch level. Even under short-distance operation, a wireless microphone’s transmitting strength changes as it is moved about (Fig. 3.). If the wireless microphone’s signal strength drops below that of the noise signal, the noise signal will immediately replace the wireless microphone signal and a sudden loud noise may come through the system. Some receivers feature noise-lock circuitry designed to prevent unwanted interference from getting into the system, but occasional noise can still get through at the moment before or after the noise-lock feature is engaged.
2. Guidelines to Eliminate Interference from Karaoke Machines Or DVD Players: a. Be selective! Choose low spurious emission Karaoke machines or DVD players: b. Select the right frequency band! Choose a wireless microphone system that operates on a different frequency band from karaoke machines or DVD players: A look at Fig. 1 shows that selecting a carrier band for your wireless system as far away as possible from the range of frequencies generated by other electronic equipment in the system is wise. There are VHF and UHF band wireless systems on the market, with the UHF being the more expensive of the two. However, the UHF band is also less vulnerable to outside interference and is the better choice for a wireless system, especially when there is known interference likely to affect the system. c. Select diversity receiving models: d. Select the latest receiver with interference elimination and adjustable sensitivity functions:
What Is the "ACT" Function in MIPRO ACT Wireless Systems? Back to Top
1. What is “ACT?” ”ACT” is the abbreviation of the world’s first "Automatic Channel Targeting" system,Mipro’s unique function which gives a foolproof, interference-free wireless system set-up in seconds! It's the most advanced way for rapidly, precisely and automatically setting a PLL receiver and transmitter to the desired frequency with only the simple touch of a button. The “ACT” function not only improves the channel adjusting procedure of the traditional PLL receiver and transmitter, it avoids the programming errors and malfunctions that are common to many wireless systems. 2. How Does the ACT Function Operate? After the receiver frequency has been selected, pressing the “ACT” button on the front panel of the receiver causes the word “ACT” to appear immediately on the LCD panel, indicating the “ACT” function has been activated. Turn on the “ACT” transmitter and point the side with the ACT logo on it toward the “ACT” button on the receiver from a distance of no more than 1 ft. (30cm.) and the transmitter will be automatically locked onto the receiver’s active frequency. Once locked, the “ACT” will disappear from the LCD panel on the receiver and the RF meter will indicate full reception of the transmitter signal, confirming the frequency on the transmitter and the receiver are correctly set up. 3. Features Of the ACT Function: Although some other manufacturers also have an “auto-scanning” feature on their wireless receivers to automatically scan for an open and interference-free channel, only MIPRO has the “ACT” function to quickly and automatically lock the transmitter onto the active receiver frequency. Whether the receiver frequency is selected manually or by scanning, the “ACT” function will precisely match the transmitter to that frequency, thereby eliminating errors in programming. Once the receiver and transmitter are set up, the selected frequency will remain locked, even when switched off and on, until they are reset. Any “ACT” transmitter can be programmed by any “ACT” receiver as long as they both operate within the same frequency band.
What Are the Advantages of Using the UHF Band? Back to Top Although wireless systems are available in both VHF (175~215MHz band) and UHF (600~1000MHz band) models, the increasingly crowded VHF bandwidth is causing more and more problems with interference from other VHF frequency sources. Consequently, many professional wireless microphone system users are progressively moving to the UHF band. In addition, many UHF systems are PLL-synthesized “frequency-agile” for even greater flexibility and ease of use. PLL-synthesized designs having tens of channels pre-set will allow users to switch to a pre-set frequency of their choice and make more non-interfering channels available for quick selection, thus helping to avoid interference problems. UHF systems are more complex in manufacturing than VHF models and are therefore more expensive, but their greater capabilities make them the recommended choice for any professional wireless application today.
Why Is a PLL-Synthesized Design Better? Back to Top Quartz-controlled wireless microphone systems have become the most popular design in recent years, both for personal use and in professional applications. Their stable performance, ease of use and economy allowed users to enjoy an acceptable level of acoustic performance. However, today’s audio professionals increasingly require simultaneous use of multiple channels and therefore need easy frequency agility, more non-interference channels and freedom from outside interference. Though quartz-control has it own unique advantages, a worldwide trend in new wireless systems shows that they are shifting away from these fixed-frequency models to programmable multi-channel and multi-function PLL-synthesized professional systems. PLL Synthesized systems use a CPU to program and control various functions in the circuit of the wireless system. As a result, individual manufacturers have developed systems that have their own unique functions and features, specifically designed to meet different operational demands. This gives more freedom of choice to users in the professional audio industry. Despite the fact that PLL systems are more expensive than quartz-controlled systems, the PLL wireless systems are the best choice for professional use today due to their multi-channel capability and better performance characteristics.
Is It Better To Have More Switchable Channels In A PLL Receiver? Back to Top A quartz-controlled receiver can receive only a single fixed channel signal, while a PLL receiver adopts a frequency synthesizer circuit design that can receive a frequency band and can freely switch to any desired working channel within that frequency band.
The numbers of switchable channels in a PLL receiver depends on the receiving frequency bandwidth and the switchable channel's interval step. The wider the bandwidth and the smaller the interval step is, the more switchable channels will be available. For example: for a PLL receiver with a 25MHz bandwidth where each channel switches by 1 MHz interval steps, then only 26 (25+1) channels will be available. If the interval step changes to 125KHz, then the switchable channels will increase to a total of 201(250.125+1). Similarly, if the interval step is changed to 25KHz, then 1001 channels are generated. For the same reason, the smaller the interval step is, the more switchable channels there will be, but is it really better to have more switchable channels available in a PLL receiver? Since the receiving channel of a PLL receiver has a fixed bandwidth, if the interval step of switchable channels is smaller than the receiving bandwidth, its center frequency will still cover within the sidebands of the receiving bandwidth and cause interference. For example: if a receiver has a 250KHz receiving bandwidth and switches channel by incremental steps of 25KHz, then 11 switchable incremental channels are available, but since all are included within the receiving bandwidth, sideband interference can occur. Consequently, it will be practical only if the interval step of adjacent switchable channels is wider than the receiving bandwidth. In other words, it is redundant to switch to .a channel having an interval step smaller than the receiving bandwidth. When multiple channels are used simultaneously, it's not easy to select the non-interference ones. Not only does each channel's own multi-harmonic waves interfere with each other, but the receiver's selectivity and sensitivity, squelch threshold…etc. are factors that can also affect potential interference. As a result, for a more advanced PLL receiver, it is not desirable to have as many switchable channels as possible, but rather to design a selected group of preset non-interference channels chosen from the switchable ones available within a certain bandwidth. This helps users rapidly switch to another "interference-free working channel" by choosing only from these pre-selected channels. All of the preset channels for MIPRO's ACT series are precisely selected so that, with the unique ACT function, just one press of a button will make the receiver automatically and rapidly scan and lock on an interference-free channel within a set of preset channels. Additionally, it will skip any channels having interference and then lock on an interference-free channel, thus solving the biggest problem for users when setting up multi-channel systems. Therefore, the best design for PLL receivers should not be determined by the numbers of switchable channels available, but by the numbers of switchable interference-free channels that can be utilized.
Why Are Condenser Wireless Microphones the Best Choice for the Reproduction Of Natural Sound? Back to Top 1. Condenser Microphones Have Superb Characteristics: For audio professionals, a top quality sound reproduction should capture the natural sound of voices and instruments accurately. Condenser microphones combine precise manufacturing technology with a sophisticated circuitry design to provide a product which best represents that natural sound in high-end audio applications. 2. Theories of Condenser vs. Dynamic Microphone Capsule Designs:
3. The Design of the Diaphragm Determines the Sound Quality: The diaphragm is the main element in a microphone capsule to detect sound pressure and convert it to electrical signals. The material and mechanical design of a diaphragm have a great influence on the characteristics of the sound quality that is captured and reproduced by a microphone. Because condenser and dynamic microphones apply different principles, the design of the diaphragm differs accordingly. As a result, each type of microphone has its own unique sound quality and characteristics. 4. Condenser Capsules Have an Extremely Wide Frequency Response: The diaphragm of a condenser microphone does not need be loaded down with a voice coil or other components and can thus be constructed of material that is ultra light and thin capable of detecting the slightest sound pressure. The output audio signals of a condenser capsule show an extremely wide frequency response that can easily extend to ultra low frequencies (under 10 Hz) as well as reaching the ultrasonic range (tens of KHz). This is far beyond a dynamic capsule's limit because its design requires the voice coil to be attached directly to the diaphragm and installed inside a magnetic field in order to convert sound pressure into an electrical signal. Since the diaphragm has to bear the weight of the voice coil, which is a hundred times heavier than itself, it can hardly maintain its vibration in sync with increasing frequency and output levels of the voice coil, especially in the higher frequencies. At the lower end of the sound spectrum, the impedance and speed of cutting through the magnetic field of the voice coil decreases as the frequency lowers. Hence, the output level at low frequencies decreases accordingly. In addition, the weight of the voice coil, the thickness of the diaphragm, and the stiffness of the capsule material itself all have their physical limits. Consequently, the frequency response of a dynamic capsule in both treble and bass, especially in the outer limits of those ranges, is facing an insurmountable technical barrier. 5. A Condenser Microphone Capsule’s Ultra Light and Thin Diaphragm Gives Unusually High Sensitivity: Because the diaphragm of a dynamic capsule has to carry a voice coil, it has a lower limitation to its thickness. This thicker diaphragm makes a dynamic capsule much less responsive to weak sounds and its output sensitivity cannot be increased due to a limited number of voice coil turns. Conversely, because the diaphragm of a condenser capsule does not have a voice coil attached, it can be made extremely thin and light. As a matter of fact, the thickness of the diaphragm in a condenser microphone is 10 times less than that of a dynamic. Utilizing this extremely thin diaphragm ensures superb frequency response, excellent sensitivity, and the ability to pick up the weakest sound. Therefore, when it comes to studio recording where natural sound and quality must be precise, clear and detailed, only condenser microphones can do the perfect job.
How to Hold a Wireless Handheld Microphone In Order to Achieve the Best Sound Performance? Back to Top It is with regret that I often see many users holding their wireless handheld microphones in various major stage, TV and concert performances using incorrect techniques. Inappropriate usage of a premium microphone can not only diminish its original superb performance characteristics and sound quality, but can even make it seem no better than an inferior quality microphone. Many audio engineers have their own microphone sound preferences and feel that they can obtain the sound they want by simply using a leading brandname of microphone coupled with their own sound adjustments. The importance of mentoring the users in the art of correctly using a microphone is often sadly overlooked. A microphone is simply a part of the complete audio system. A satisfactory sound cannot be achieved, even when using the most expensive microphones, without a thorough understanding of the proper usage and adjustment of the microphone as well as the other related audio components. The same principle applies in driving an expensive sports car. If drivers are not fully aware of a car's unique characteristics and operation, they will be unable to get the maximum performance out of the car. Below are a few recommendations to enhance the sound of a microphone: Many performers tend to hold the microphone by the grille (see fig.1A&1B). Unfortunately, this position seriously degrades both the sound quality and directionality of a microphone. Even the most expensive microphone will have its original sound quality compromised by this method. Grabbing a microphone by the grille will isolate the capsule's acoustic resonance circuit and/or change the capsule resonator's frequency. This results in an inferior performance in both frequency response and the separation of directionality. In addition, a palm's sound-focusing effect will tend to strengthen resonances in certain frequencies and can cause unwanted feedback.
Although a wireless microphone is convenient and safe to use without those tangling cables, users often negate their inherent superior characteristics by the use of improper techniques in holding the microphone. Therefore, to achieve the best sound possible, a microphone user must learn the proper techniques, which fortunately are rather simple. The single most important principal to remember is to always hold the microphone by its housing or body instead of covering the microphone grill (see fig. 2).
2. Do Not Hold Two Microphones in One Hand: It is very surprising to see some users holding two or more microphones in one hand at various performances (see fig. 3). Unfortunately, this is an incorrect technique regardless of how "cool" it looks or even if requested by a "creative" sound engineer, which is a highly questionable practice at best.
Holding two different frequency transmitters in close proximity can cause intermodulation interference (see fig.4A, 4B). This is especially risky in multi-channel system operations where issues such as interference and unstable reception can easily cause the audio quality to deteriorate. Close proximity causes interference in a microphone's audio frequency phase and directionality, and can destroy a microphone's default characteristics, apart from just RF interference.
When both microphones' audio signals are in phase, it adds up to two microphones' audio output and a subsequent sudden increase of the amplifier volume, thus causing feedback (see fig. 5A.). Conversely, if the signals are out of phase, they will offset each other's output and result in insufficient volume (see fig. 5B). When two microphones get close to each other, their directionality will interfere with each other and destroy their default directionality. Performance tends to get worse as the distance between two microphones diminishes. Therefore, users should avoid the practice of holding two or more microphones simultaneously in one hand to prevent an undesirable loss in output volume, frequency response, and directionality.
Some users may be thinking that holding more microphones in one hand can prevent the embarrassment of a microphone failure. In fact, however, holding more microphones in one hand will just result in a significant change in the system performance ~ for the worse. Replacement microphones are a better solution than holding more microphones, if the sole purpose is to avoid microphone failure. If more microphones need to be used simultaneously, then keep one microphone at least 30 cm away from the others to reduce the likelihood of detrimental changes in performance. 3. Keep a Proper Distance between the wireless Microphone and Mouth! A proper technique is required for using directional microphones because the distance between the microphone and your mouth has a significant impact on sensitivity and performance. There is an inverse relationship between microphone sensitivity and the distance from the mouth to the microphone. Consequently, performers with a "weaker" sound level cannot expect to hold the microphone too far away from their mouth and compensate by turning up the amplifier volume to increase the sound level as this will easily cause feedback. In contrast, performers with a "louder" sound level should not hold the microphone too close as this will easily result in causing the amplifier system to have overload distortion.
Furthermore, a large-diaphragm directional microphone has a very distinct proximity effect. When the microphone is close to the mouth, the bass response is strengthened as the distance gets closer (see fig. 6A). Therefore, if a performer's sound is insufficient in bass response, they can hold the microphone closer and use the proximity effect to help compensate for the lower bass level. Conversely, if a performer's voice is too heavy in the bass register, increasing the distance between the microphone and their mouth will decrease the proximity effect and reduce the bass response, thus making their voice become clearer (see figure 6B). The distance between the microphone and the mouth also has a significant effect on "popping noises". This is especially severe when you are using a microphone that has high sensitivity and a stronger low-frequency response. To reduce this problem, one must be very careful to adjust the microphone to an optimal operating distance and select a microphone that has excellent "popping" noise prevention. Most premium and professional microphones have a highly effective design to eliminate "popping" noises. As described above, the sound of two identical microphones will be significantly affected just by how they are being held. Practicing a proper holding technique and learning to use the proximity effect that best suits the performer's voice should guarantee the most desirable volume and tone while avoiding annoying "popping" noises. Therefore, singers that use wireless microphones should strive to get the best performance possible by learning these techniques to make the best use of a microphone's performance characteristics.
|
||||||||||||||||||||||||||||||||||||||||||||||||||
After they are received by the antennas, audio signals are demodulated and sent out via the signal detection circuitry, then filtered and demodulated into signals of audio code through the Pilotone Control Circuit. Subsequently, the signals are sent to the Audio Frequency Output Switch, keeping the switch open while sending out the audio signal. 
Although there are lower cost “non-diversity” systems on the market, their limitations in actual performance limit their usefulness in professional applications where drop-outs and unwanted noises could create a real problem. The greater dependability, sound quality and performance of Mipro’s “true-diversity” system makes it the only logical choice for professional audio applications. 
