Microphones. The importance of sound in quality productions.
Sound. An essential, elegant, discreet element that plays a crucial role in our audiovisual productions, determining perceived quality of our production in far greater extent that the attention sometimes given to it. Text: Luis Pavía.
We have all felt at some point uncomfortable and even have lost interest in a content we were keen to enjoy because of low-quality sound. There are countless reasons why final audio in a production can be faulty. In order to prevent this, in this occasion we will devote our article to the first step of the process: capture. As it is the case in many other instances, the better the original, the smoother and more solid the whole subsequent process and, therefore, the better the end results.
Without dwelling too much in history, the fact is that capture has always relied on a transducer, a device capable of converting sound into electricity, this latter element being subject to recording. And, what is sound? In summary, it is multiple and succeeding changes in air pressure under various amplitude and frequency patterns in acoustic waves that can be perceived by the human ear, generically in a range between 20 and 20,000 Hz.
A microphone is a tool in charge of carrying such conversion as cleanly as possible in order to make sound accessible for recording, processing and playback with the highest fidelity available. Having undergone a significant evolution from its beginnings, progress has not managed to get the same media impact as other elements that are part of production, such as camera sensors or image recording formats.
If we wonder what the best microphone we know of is… the answer is obvious: our ears. But they come equipped with a “processing” and filtering system that enable us to do some wonders such as perceiving and discriminating sounds of highly varying levels (volume) at the same time, which for example allows us to understand and follow conversations in very noisy environments. But that is something performed by our own brain and falls outside the scope of our article, not to mention the different sensitiveness each individual has.
Microphones have their own features and qualities (sensitivity, response curves, etc.), all of them focusing on a single goal: provide the best possible ‘image’ of the sound to be recorded. As any other electronic devices, microphones also generate their own ‘noise’ while doing their job, so there are many aspects to consider when it comes to choosing a microphone for a particular task. Not all of them are good for every purpose and our responsibility lies in knowing how to choose the most suitable device for each situation.
The ambitious purpose of our today’s content is identifying the best microphone without making any reference to brands or models. Evidently, the best microphone is the one “you have around”, but we are going to devote these lines to analyzing the significance of each particular feature. Therefore, and depending of each project’s particular purpose, we will be able to select that microphone that we “will have around”, which will then be the most suitable in the situation at hand.
We will analyze their various features and their impact on our results; and classify, based on specifications, those features that will be easily found published by manufacturers. Let’s not lose sight of the fact that each model is the result of various combinations of parameters. Each combination has distinct advantages and drawbacks and this will both allow and force us to make the most appropriate choice in each circumstance.
We now begin with a brief review of some basic technical specifications that we need to know in order to be able to better assess all notions covered throughout this article. These features are: “sensitivity”, “dynamic range”, “frequency response” and “signal/noise ratio”. Engineers forgive us, but we will not cover in depth the physical and mathematical concepts for the sake of easier explanations in certain instances.
Sensitivity or transfer factor indicates a microphone’s capacity for converting acoustic pressure into electric power. The higher the value, the cleaner the final output and the less amount of processing that shall be required for further handling. It is calculated in milivolts by pascal and converted to decibels (dB) in respect to a pattern of reference. Be reminded that dB is a logarithmic scale, so every 3-decibel change equals to a double or half factor, depending on whether it is increasing or decreasing. Therefore, just 60 decibels already equal to a multiplying factor of about one million. This means that apparently small differences in values result in very significant changes in behaviour. Higher values –as we are normally dealing with negative figures here-, the less negative (closer to zero) a number is, mean greater sensitivity. As the pattern of reference in this specification is a standard one, values can be compared among various microphones provided said pattern is adhered to. Surprisingly enough, we will now discover that using the microphone that has the highest sensitivity is not always the best choice.
Dynamic range is the difference between the lowest and the highest level a microphone is capable of acknowledging without distorting sound, or at least when keeping distortion within certain limits. It is also expressed in dB and, as these are always positive values, we want them to be as high as possible in this instance. Although in this case the problem is that each manufacturer might use a different distortion pattern, thus turning comparison of values here into something scarcely meaningful. As a generic reference suffice it to say that average dynamic range of perception is about 80 dB for the human ear.
Response frequency is the range of frequencies a microphone is able to capture and its response curve represents the sensitivity offered to each one of these various frequencies. Usually, response is not perfectly uniform and, therefore, depending on the relevant purpose, a microphone featuring a limited range can be the perfect choice in some instances, even if it is only operational in very specific, narrow ranges. It is easy to understand that our needs are not the same for recording piano playback, where good response is required for a very wide, continuous range of frequencies, as for human voice, which requires a more limited range; or a bass drum, in which case range is even narrower and biased towards low frequencies. In this regard, the standardized pattern for the human ear is within a range running from 20 to 20,000 Hz.
Signal/noise ratio is another key feature. As a rate between two values, it is also expressed in dB, and provides an idea of how much separation there is between the noise generated by the electronics intrinsic to the microphone itself when not capturing any sound and the signal output provided when sound is being captured. In this instance it is desirable to achieve the highest value possible and, as it is a reference in respect of itself, values should certainly be easily comparable between the various manufacturers.
There are other features such as impedance, which being important when it comes to choosing what equipment the microphone will be plugged into, have not a really direct impact on sound output; although it can be said, as a general rule, that microphones of higher quality are usually classified as ‘low impedance’, with values ranging between 50 and 600 ohms. This value is even lower -200 ohms at most- in professional environments.
Once we have reviewed specifications and refreshed a number of concepts, we will delve now in the main features that, properly combined with said specifications, will help us to select the most suitable microphone for each particular circumstance.
Let’s begin by ‘microphone type’, which makes reference to the technology used by the transducer, that is, the device that captures and converts the acoustic energy into electrical energy, the capsule itself. The three most usual types are: Condenser, electret and dynamic.
Condenser microphones are normally the ones boasting a higher sensitivity as the mass of the membrane that has to be moved by air waves is very small and therefore, these offer excellent response. Although the downside to this is that they require some electronics that in turn need power supply in order to operate and amplify their minimal signal and this can result in some noise. They typically require a battery or an external power source, the so-called phantom, which comes from the camera or a preamplifier through the connection cable itself. They generate a high-quality signal and come in a very broad range of applications and prices. Advantages offered are excellent sound quality featuring uniform response in a wide range of frequencies, but a drawback is that they are very fragile in extreme temperature or humidity environments, as well as the maximum sound levels they are able to handle.
Electret microphones, sometimes seen as a subtype within the condenser type, are characterized by the fact that the power needed for operation comes from a permanent ferroelectric charge provided by their own building material. In former times they did not offer quite the same quality as condenser microphones, but nowadays the best in their class are comparable. They are easy to manufacture and relatively low-cost for acceptable performance, so they are nowadays the most frequently used ones for mobile phones, laptop computers and a wide range of small devices. In this instance, quality range can be much wider and we ourselves must assess whether a given model meets our requirements, as well as all other parameters being considered. Although these do not require polarization voltage, it is also quite common that devices offering higher quality feature a built-in preamplifier in the capsule in order to make up for their lower native sensitivity. The fact that they require power supply must not lead us to confuse them with the condenser type.
Last, dynamic microphones are polarized by electromagnetic induction. They have a large amount of favourable features, as for instance their greater robustness -because of their simpler build-, high gain, and strong resilience to extreme temperature and humidity conditions. However, the feature to highlight here is a good sound quality versus acoustic levels much higher than other types of microphones, with no distortion or overload whatsoever.
As a general rule, condenser microphones offer much higher sensitiveness than dynamic microphones, even exceeding 10 dB. However, we will often choose one type or another also taking into account our work environment: generally speaking, a condenser microphone will achieve better sound quality provided it is used in a controlled environment such as a recording studio or a concert hall. However, the harsher the conditions, the more versatile and safer the dynamic microphone, as it is the case with live stages or rock venues, just to name a few examples.
The following feature we will cover is the ‘polar pattern’. This term makes reference to the areas from which we are able to capture sound; or, in other words, sensitivity depending on direction. This is typically represented by a graph showing concentric circles where a curve in different shapes indicates greater sensitivity the further away from the centre, if we picture a microphone centred and pointing towards to 0º mark. Again, three major types can be found: omnidirectional, cardioid and unidirectional.
A microphone is said to be omnidirectional when it captures equally all sounds coming from any direction. Logically, this is ideal for capturing ambient sound in a natural fashion. On the other hand, an unidirectional microphone has excellent capabilities for picking up only sound coming from the direction towards which it is pointing, almost completely eliminating any sounds that fall outside the relevant line. This enables a clear separation between the centre of action and the rest of the environment. A cardioid microphone receives its name from the mathematical curve that represents the device’s behaviour, which is in between the first two types. This microphone is capable of progressively muffling sounds as they are more distant from the central line, but keeping a lessened part of the sound captured from the sides. Based on the various balances kept between front, side and rear in the cardioid type, there are subtypes called subcardioid, supercardioid and hypercardioid.
With these options alone, we have more than enough as to establish what we need to focus on, knowing the type of situation we must face. But there is more to it.
Based on their particular use, they can be classified as integrated, handheld, shotgun, lavalier and headset microphones. An integrated microphone is, as its own name indicates, integrated in another device –i.e. a video camera- in which case there is very little we can chose from. The widest range is found among handheld microphones. This group also encompasses those usually found in different table stands, etc. They come in nearly all types that we have so far examined, so we must really analyze them in depth before finding the kind that will be most adequate to our needs.
And now, be warned before going into the next group, because confusing a shotgun microphone with a directional microphone is easy. Shotgun microphones are normally those external microphones found in video cameras –usually of cylinder, or elongated shape- but not necessarily unidirectional, as they can also be cardioid microphones. This same type of microphone, both in unidirectional and in cardioid variants, is also found inside a large case that envelops the microphone at the end of a boom in studios and in shootings. So, we should not confuse shape with function. Unidirectional microphones are normally of shotgun type, even with a parabola at the base, although not all shotgun microphones are unidirectional.
Lavalier microphones are those small microphones typically of vocal range that are attached by means of a small clip to the clothing, being their main purpose to let users have their hands free. The risk involved is picking up noise from the clothes themselves, particularly if the device comes in contact with them or if the relevant person touches it. Also with the purpose of freeing our hands while avoiding contact and also intended for more intense physical activity, such as it may be the case with singers or sportspeople, we have headset microphones, which are directly placed in front of the mouth or sticking to the cheek by means of a set placed on the head or neck. Strangely enough, lavalier and headset microphones are the types providing better results the less sensitive they are, simply because the sound source is so close and therefore this eliminates such need. This also prevents capturing ambient sounds, which are normally not necessary in these uses.
But, we still need to convey the microphone’s signal to the mixer, the preamplifier or the recorder that is to handle that signal. And here we must open a new chapter.
Conversion of acoustic energy is an analogue process that results in a signal of very low power, so its reach is really limited unless we amplify it in some way. And this is the reason why some microphones include a small preamplifier with the aim of homogenizing signals, which are typically handled in the range of around 100 milivolts, a figure clearly lower than traditional line signals, which range around 1 volt, 10 times greater, as long as we stay within the environment of analogue audio.
If we need to transfer said signals by means of cables, we find two kinds of essential connections: those balanced through XLR connectors, or unbalanced, which feature jack or minijack connectors. The benefit of balanced signals used in professional environments lies on the fact that they have a reference system that enables the filtering of noise and electromagnetic interference that would not be otherwise available. Therefore, multiple balanced signals can easily cover many yards by means of mixed cables with no quality loss, whereas unbalanced signals are much more vulnerable and are only useful in very short distances.
By keeping wired connections, we could even go a step further and turn them digital, which would make transport more secure and even less vulnerable to interference. By just using a small analogue/digital converter and connecting it to a PC or an amplifier by means of a USB port for a generic use. Or even for a more professional use, convert those signals and integrate them in an IP environment such as Dante or Ravena, although in spite of the fact that this is a perfectly valid option being increasingly used in professional environments, it falls outside the scope of today’s article.
What our content does cover, however, is wireless transport, where, once again, both analogue and digital options are available. And a key alert in the area of transmission, and most particularly with regards to microphones that for quite a long time have been making use of UHF frequencies: yes, precisely those mid-range frequencies among channels used in former times for TV, which achieved such a good result for this transfer of wireless microphony. And we say ‘former times’ because the digital dividend, that is, an international administrative agreement by which frequencies that had been used in former times by TV channels are now used for gradually increasing –in several stages- bandwidth of 4G and 5G data channels through mobile telephony.
And we should at this point draw the attention to the fact that many devices may soon go out of order, if they have not already done so. Channels 21 to 69 of the UHF band have made use of frequencies ranging between 470 to 862 MHz for TV services. Gaps left by those used to host short-range wireless microphony transmissions.
This year 2020 has seen the relocation of the whole frequency band above 694 MHz (channels 49 to 69) to 4G and 5G services, so any microphone working in this range will surely be severely affected. Therefore, we strongly recommend to those of you who are thinking about purchasing any microphony system, to make sure it works in any channel below number 48, meaning any frequency below 694 MHz.
Having expressed this concern and getting back to wireless transmission, there is yet another possibility in which ample offering is beginning to grow, with systems based on the 2.4 GHz band, the same one as Wi-Fi, but featuring less risk of interference as these systems have their own protocols for identification and channel skip.
An aspect that is hardly known and resulting in significant differences in price –and in quality as well- between various equipment alternatives, are wireless transmission systems that recreate the notion of the balance cable. The receiver is actually two receivers that work simultaneously and in parallel for a single signal. What does this achieve? When two receivers get exactly the same thing, it is obvious that the signal is excellent. But differences do exist. By means of built-in filtering and discrimination electronics, defects and interferences can be removed, resulting in a completely clean transmission, and one boasting much higher quality than systems that are not equipped with this capability.
With regards to wireless transmission for microphony, transmitters can be integrated within the microphone’s own body –in handheld devices- or come in the shape of a pack that can be attached to the microphone’s XLR connector or even the typical beltpack for lavalier or headset microphones. In this case, they always broadcast on a single channel, which synchronizes with the relevant receiver, although the most recent models are capable of ‘talking’ with one another to switch channels when the need of avoiding interference arises.
And in receivers, variety is much greater. They come in the form of a battery-powered pack being attached to a camera, or are powered by the camera itself to be completely mobile. They can also be a desktop device for use in recording studios, sets or stages with no need to worry about power because they will be plugged to an outlet. The more economical receivers are single-channel ones, while high-end devices feature such dual tuner so as to ensure the best sound quality, as we mentioned above. Because we should not confuse them with a different kind of receivers that feature two tuners, but in this case with the aim of receiving in the same device signals of two different broadcasters.
In sum, a comprehensive, immense range of possibilities, taking into account capture technologies, recording and response capabilities, physical configurations and transmission methods in order to find the most suitable device for any need.
And so we have reached the end of our content and have met our goal of not mentioning brands, models or prices. The purpose was neither to tell you what microphone you should use or to find the only one that will work in every occasion, which of course is not possible. The intention was just to provide you with some guidelines for understanding features, thus enabling you to face any project with the best assurance for success, as there is no perfect tool, but a tool suitable for a particular requirement. And in view of the speed at which the market is moving, novelties launched by manufacturers, the huge variety of prices and changes, as well as special deals, any specific details we might give you would become outdated in a matter of a few weeks.
What never becomes outdated is knowledge. And should this content be of use to enable your next production have improved sound quality and therefore, result in a better final product, we will feel a part to your success. Thank you for carrying us with you.