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A.C. Resource Centre

In this section you will find lots of information that you may find useful. Click on each header to see the information.

  • Dynamic Vs Condenser Microphones

    Dynamic microphones have a moving coil and are more durable and robust than condenser mics. They can take high amounts of sound pressure levels making them ideal for live stage use and on instruments with a high output. The diaphragm material is heavier than a condenser and carries the weight of the voice coil, so responds a little slower and is harder to move. There’s no amplifier in it so the microphone itself is less sensitive.

    The sound enters through the microphone grill, moves the copper, wire wound voice coil in and out of the magnetic field and then creates a small voltage at the output.

    Condenser (capacitor) microphones are very sensitive and require phantom power. The sound enters through the microphone grill, moves the sound plates and sends the sound through the amplifier to create an output. They have an amplifier inside them so they can pick up the slightest sounds and capture more detail. The diaphragm is very easy to move and responds much quicker than a dynamic mic, ideal for vocals, cymbals, finger picking and anything needing a full frequency response.

    Shure offer this great guide to tranducer types -

  • Alternate Microphone Types

    An Electret microphone is similar to a condenser but eliminates the need for a polarizing power supply (phantom power) by using a permanently charged material. An Electret microphone usually requires a battery to power the internal circuitry. This type of microphone can often be powered by phantom power.

    A Ribbon (velocity) microphone is a type of microphone that uses a thin aluminium ribbon placed between the poles of a magnet to produce a voltage by electromagnetic induction. Ribbon microphones typically have a figure of eight pickup pattern, meaning they pick up sounds equally well from either side of the microphone. Most ribbon mics are incredibly fragile and can be damaged by high sound pressure levels meaning if you were to drop the mic or blow into it, it will permanently damage the microphone’s ribbon. Phantom power can also destroy a traditional ribbon mic.

    Ribbon mics have an uncanny way of “hearing” sound in a very similar way to human ears and can capture audio in a very realistic way. Ribbon mics tend to have a very low output, meaning they work best when used with a quality mic pre-amp with plenty of gain (boost). A good ribbon mic used as overheads or room mics will do a stunning job of capturing your drum kit in the studio. Like our human ears, ribbon mics tend to roll off sharply after about 10KHz and will sound fantastic on a guitar amplifier, eliminating any “fizz” in the recording.

  • Polar Patterns Explained

    A polar pattern is how well a microphone picks up sounds from different directions. The polar pattern influences which microphone you use in different situations. Here’s a run down of the various patterns and what they pick up:

    • Cardioid
      The well known heart shape pattern picks up what’s directly in front of the microphone making it the best choice for live performances where stage monitors are being used.
    • Super Cardioid
      The heart shaped pattern with a bubble at the rear. These pick up what is directly in front of the microphone and also have some pickup at the rear.
    • Omni Directional
      The spherical shape, picking up sound from all angles. Responds equally all around the microphone making it prone to feedback.
    • Bi Directional
      The figure of eight shape picks up in front and to the rear of the microphone but not the sides.

    Shure explain polar patterns further -

  • Small and Large Diaphragms

    A small diaphragm microphone has more articulation, responds to sound quicker and is crisper than a large diaphragm mic.
    A large diaphragm microphone is not as quick to respond as small diaphragm mics, has a more natural and warm sound, making it better for vocals.

  • Microphone Techniques

  • What is phantom power?

    Phantom power is needed for condenser microphones and some DI Boxes. You will see phantom power on most mixers, audio interfaces and pre amps where they have the ability to send +48v to a condenser microphone which needs power. If you wish to record or perform using a condenser microphone you’ll need a device which can provide phantom power.

  • Wireless Systems and Frequencies

    Wireless microphones can come in handheld, headset or lavalier microphone form and normally consist of a transmitter and a receiver. Not only used for stage, wireless microphone systems are used by fitness instructors, schools, presenters and houses of worship. For a guitarist it frees their environment of cables and allows them the freedom to explore the stage. Using a guitar bug or instrument cable with a bodypack, the wireless guitar systems are simple to set up and ready to go

    Sennheiser G3

    • Range GB 606 - 648MHz (Channel 38) - Requires a license
    • Range E 823 - 865MHz (Channel 70) - License free
    • Range C 734 - 776MHz - Requires a license
    • Range B 626 - 668MHz - Requires a license
    • Range G 566 - 608MHz - Requires a license
    • Range A 516 - 558MHz - Requires a license


    • Band D 614-686MHz (Channel 38) - Requires a license 
    • Band F 863-865 (Channel 70) - License free


    • K3E 606 - 630MHz (Channel 38) Requires a license
    • S6 838 - 865MHz (Channel 70) License free
    • Z2 2.4GHz - License free


    • Channel E1 863.125 MHz (Channel 70) - License free
    • Channel E2 863.625 MHz (Channel 70) - License free
    • Channel E3 864.500 MHz (Channel 70) - License free
    • Channel E4 864.875 MHz (Channel 70) - License free


    • Band D 863 - 864 (Channel 70) License free
    • Band U 606 - 629 (Channel 38) Requires a license


    • Band D2U 854 - 865MHz (Channel 70) License free
    • Band G2U 606 - 622MHz (Channel 38) Requires a license

    Shure have some great information on wireless microphones here -

  • Wireless Microphone Frequency Guide

    Resource: ?(PMSE, Programme Making and Special Events)

    There are two types of UK Wireless Microphone Licence.

    UHF - UK wide shared access to Channel 38 (606.500-613.500 MHz) internally or externally and licensed on a non-protected basis for either one or two years.

    Users can typically achieve 10 radio microphones in this range operating in the same place at the same time. However this can differ case by case.

    Access is not restricted to specific frequencies and users can re tune within the stated range to any usable frequency.

    VHF - UK wide shared access to 15 spot frequencies in the range 175.250 to 209.800 MHz internally or externally and licensed on a non-protected basis for one year only.

    These licences are popular due to the one off purchase with no requirement to notify us of where or when these channels are being used. However as the channels are shared users must be prepared to retune to alternative frequencies if interference from other local users is experienced.

    Standard Licences are issued when a user wishes to access frequencies that are coordinated with other users or uses.

    This licence is used for equipment such as radio microphones, in ear monitors or wireless cameras.

    Coordination could take place with other local PMSE frequency users, or for some equipment it will be coordinated to ensure there is no television transmitting that will affect the use.

    These licences require users to book on a location by location, date by date basis. Frequencies are booked anywhere between 15 minutes to one year, however annual, long term of fixed site access is usually only permitted for the permanent resident or owner of the site.

    Risk of interference on these frequencies is minimal due to the coordination process, however we will support instances  of interefence on these channels.

    The use of Channel 38 covers you for multiple units providing they sit within the boundaries of Channel 38. The range for Channel 38 is from 606.500 to 613.500 MHz. Anything outside of this range is not covered by the licence.

    Access to Chennal 38 is not location specific and covers you for multiple locations simultaneously UK wide.

    The power on limits on Channel 38 is 10mw for handhelds and 50mw for body worn transmitters internally or externally.

    Users can utliise as many frequencies that can practically fit within the range, intermediation and adjacent frequency use will the prime factors affecting this figure.

    Practically speaking you could fit 8-10 frequencies into this range depending on equipment deployment, however if the devices are physically spaced apart more can be achieved without intermediation. 

    The frequencies in the Channel 38 guard bands ? 606.000-606.500 and 613.500-614.000 MHz are illegal to use and are not covered by the licence.

    Some equipment that is manufactured can tune into frequencies that do not require a licence to operate. There are several licence exempt areas for PMSE use.

    The UHF licence exempt range is 863.100-864.900 MHz. This is within Channel 70.

    Channel 70 is adjacent to use of mobile in the 800 MHz band. There should not be any interference however this is the risk taken with the licence exempt channels.

    The power on channel 70 is limited to 10mw for handhelds and 50mw for body worn transmitters both internally and externally.

    There is no limitation to how many frequencies can used in this channel as long as users stay within the confines of the band. On average users would probably be able to use four units at one time.

    There are currently no plans to remove access to Channel 70 it will continue to be licence exempt for PMSE users.

    There is also a VHF licence exempt range which runs from 173.700-175.10MHz.

    A licence exempt WiFi band runs from 2.400-2.4835GHz and is free to use for audio equipment below 10Mw, manufacturers suggest that up to 70 radio microphones could be used at one time in the range, however there are many other uses of this band such as WiFi networks, Bluetooth short range links and microwaves.

    For more information on wireless microphone licences you can visit the official Ofcom website at or the official PMSE website at

  • What is digital wireless?

    Digital wireless runs on 2.4 GHz and is designed to work in the wifi space meaning it’s not affected by interference from mobile phones and other transmissions.

    For an overview, see our YouTube channel:

  • What’s the difference between passive and active speakers?

    Passive speakers need to be connected to an external amp to work. The amp will then need to be connected to your mixer.
    Active speakers (also known as powered) have an internal amp and can connect directly to your mixer.

    With modern day high powered, low weight power amp modules, active speakers have become more popular and convenient to run with a PA system. Active speakers are more often than not bi-amped, meaning they have two independent internal amplifiers powering the woofer and the tweeter separately. This makes a much more efficient system as each amp can dedicate all its resources to a specific area of sound, i.e. bass and treble. Most active speakers have an internal control network so the crossover points for the bi-amping and protection limiting is all automatically looked after for you in the back ground.

  • What’s the difference between an analogue and digital mixer?

    Yamaha offer the following information from

    Digital and Analogue Mixers

    The mixing console or "mixer" is a central component of most sound systems. In fact, the mixer used will have a large influence on the operability and efficiency of the entire system. One of the first decisions that will have to be made when designing a new sound system is whether a digital or analogue mixer will be used.

    Digital Mixers are Rapidly Gaining Ground

    Described in the simplest terms, the difference between analogue and digital mixers is whether audio signals are internally processed in their original analogue form or converted to and processed in digital form. Digital mixers are rapidly gaining popularity for their convenience, expandability, and resistance to noise. But there are still situations in which analogue is preferred. Let's take a look at the features of each.

    Digital Mixer Features

    Five of the most important features of digital mixers are listed below.

    (1) Settings can be pre-programmed and recalled when necessary.

    Most digital mixers feature some kind of memory into which settings can be stored and then instantly recalled whenever they are needed. This can be a tremendous advantage in a banquet hall facility for example, where the required settings might change frequently for different types of events and different room configurations. Even if some fine tuning is required, the ability to simply recall a complete set of basic parameters that are close to what is needed can dramatically reduce the time and effort required to set up for an event. And if a mistake is made, it's easy to revert to the basic settings.

    (2) Mixing and processing features that only digital can provide

    Digital technology has enabled the development of a number of mixing functions that were simply not available in analogue systems. Automatic feedback suppression is one example. Automatic "ducking" that decreases the BGM level while an announcement is being made is another.
    Many digital mixers also feature built in signal processing functions such as effects that are designed to suit the mixer's intended applications. This makes it unnecessary to purchase extra external signal processing devices, thus significantly reducing overall system cost as well as installation space. This is a radical departure from analogue systems for which additional equipment had to be purchased and installed to provide the signal processing functions required by each individual application. There are analogue mixers that include some built-in processing functions, but unlike digital mixers in which all of the necessary processing can be implemented through software, additional processing capability has a direct influence on the cost and physical size of an analogue mixer. For the same mixing and processing capabilities, a digital mixer will almost always offer superior economy.

    (3) Expansion and external devices

    Expandable digital mixers make it possible to connect to a wide variety of external devices. Touch panel controllers, for example, can make day-to-day operation of a specified set of frequently used parameters easy for even inexperienced users, while keeping parameters that should not be changed hidden.

    (4) Noise-resistant digital transmission

    A sound system that is based on a digital mixer that uses digital transmission for audio signals will be highly resistant to induced noise. Since noise becomes more of a problem with longer transmission distances, the benefits of digital transmission in an audio installation increase as the size of the facility increases.

    (5) Multiple functions in small spaces

    Although analogue mixers usually have one control per function, in a digital mixer it is possible to assign numerous functions to a single control, with function switching either via physical controls or virtual controls on a display. This makes it possible to pack a large number of functions into a relatively small space. If you compare analogue and digital mixers that offer the same number of channels, you'll see that the digital mixers tend to be significantly smaller.

    Analogue Mixer Features

    Analogue mixers have two main advantages.

    (1) Lower cost for a limited set of features

    If only a few channels with a basic set of mixing features are required, a simple analogue mixer may be a more economical choice than a digital mixer.

    (2) Easy operation for first-time users

    As mentioned above, analogue mixers usually have one control per function, all of which are visible and directly accessible via the control panel. The control layout logically follows the mixer's signal flow and is therefore relatively easy to understand. This type of logical, easy operation can be an advantage in public halls and schools, for example, where a variety of people, some having little or no previous experience, may need to operate the system. In such situations it may be necessary to protect controls and functions that should not be changed with security covers.

    That covers the basic differences between digital and analogue mixers. Depending on the application, the choice of a digital or analogue mixer can make a large difference in the operability and overall economy of the system.

  • Guide to Mixing

    Soundcraft have some great videos on mixing which we’ve added to our YouTube playlist. See the following link:

  • What are pre amplifiers?

    A preamplifier will boost a weak signal generated by a microphone or instrument so that it's a suitable level for further mixing and processing. Most mixers with microphone inputs will have preamps built in. On a mixer, to adjust the gain range of the preamplifier you can use the 'trim' or 'gain' knob. If you're using a mixer with only line inputs you cannot plug a microphone in as there are no preamps and therefore, won't be enough gain. You can use an external pre amp (which can be battery powered) to boost the signal before going into the mixer. The quality and design of a microphone pre-amp will have a huge impact of the overall result you will achieve from your microphone. Certain mic pre designs will help add both warmth and character to your sound.

  • What are power amplifiers?

    A power amplifier is used when using passive speakers as you need to increase the power of an audio signal from the mixer to the speakers. This increase in power is achieved by increasing the input signals voltage from roughly 1 volt and only a few milliamps to roughly 70 volts and a much higher current which can then drive a speaker.

    Power amps are normally quite basic, especially when compared to hi-fi amps and typically have a line level input, high level output, volume control and power switch. You can have a power amp built into a mixer; this is called a powered mixer.

  • Reducing feedback on stage

    Setting up for a gig can be stressful enough without having to combat feedback once you turn everything on! Wireless microphones tend to suffer more from feedback as the performer is able to move freely and is in danger of moving in front of the speakers.

    To combat feedback, try rehearsing with your full PA set up (including any stage monitors you may use) to establish where the main feedback points are. This way you'll know which spots to avoid when in a live situation. If your singer holds the microphone quite a distance away from their mouth, try getting them to hold the mic closer so you can reduce the amount of gain on the mixer.

    If you are still having issues with feedback, try aiming your stage monitors at the least sensitive area of the microphone (depending on its polar pattern). Playing smaller venues can be an issue as you don't have the room for your normal set up. Sometimes you may end up with microphones in front of speakers and stage monitors to the side of the stage directed at the front of the microphones. In these circumstances you'd need to keep the gain down and try to stand closer to the mic when singing. You should seriously research your microphone purchase if you know you'll be playing smaller venues as the polar patterns can have a huge influence on the amount of feedback. The safest option for live stage use is a cardioid as these are least sensitive at the back of the microphone, making them easier to use with stage monitors.

    To reduce feedback for professional use, you should use a graphic equalizer to "EQ the room". Graphic EQ's may be a physical piece of outboard equipment or part of the built-in software on a digital console. Either way, the EQ would preferable have 31 bands that have a bandwidth of 1/3 octave. This EQ would then be placed across the main left and right outputs of your mixer.

    The principle:
    All rooms and acoustic environments will have frequency peaks. As you increase the volume of the PA system these peaks will reach the room's "feedback threshold", first giving you the screech, boom or whistling sound we are all familiar with. If the feedback has a higher pitch, slowly turn down one of the higher frequency bands on the graphic EQ. You will know when you have the correct band as the feedback will suddenly disappear. Bear in mind that what your human ears may perceive as a super high frequency may actually only be around 2 to 3kHz.

    As you increase the volume further you may encounter a different "note" of whistle. If the note sounds lower then turn down a lower band on the EQ until you find the one that makes the feedback disappear.

    Eventually you will end up with a visual "graph" of the EQ, with all the frequency peaks that are in that particular room... hence the name "Graphic Equalizer".

  • Choosing the right studio monitors

    There are many fantastic studio monitors these days from various brands but how do you know what to choose? Let us help you make your decision...

    Studio monitors are designed to help you get the most out of your mix. As you're creating/ recording music you want a truly honest sound with the least amount of colour. This ensures your mix will sound the best it can on multiple sound devices, eg. Radio, MP3 players, CD's etc? You'll have probably heard the term 'flat response' mentioned when researching studio monitors, this means that every frequency range should respond evenly.

    The pair of monitors you choose to do this depends on the following:
    Size of the room you're in ? The smaller the room, the smaller the monitors should be. If you were to purchase a pair of large studio monitors that can handle large amounts of bass, the bass would bounce around the room and may leave you overcompensating for this in your mix. Sometimes bigger is not better and smaller monitors should be considered.

    What sort of music you're recording - For acoustic music that doesn't need much bass, smaller monitors are more than enough. Larger monitors are better suited to producers who want to have more clarity from their bottom end and use large amounts of bass frequencies.

  • In Ear Monitoring Explained

  • Home Recording

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