8. Terminology

The reverberation generated by reflection of sound within a room allows our hearing to gain an impression of the size and specific characters of the room. Reverberation is typically divided into two stages, the early reflections and the more diffuse reverberation proper. The time and volume relations of the early reflections indicate the distance from the source of sound, whilethe reverberation supplies the spatial impression. In pop and rock music production, sound is recorded as "dry" as possible (in an acoustically treated studio), and reverb is added during audio mixing. This makes it much easier to compose a harmonious whole from many different tracks.

This is an amplification method using multiple amplifiers connected to a speaker cabinet in such a way that individual amps drive individual speakers - this means that the crossover is placed before the amplifier stage rather than after. Active speakers use this system by default, but passive speakers can be driven with multiple external amps and active crossovers in this manner, and this is the method typically used with larger monitoring setups. Bi-amping describes a 2-way system, tri-amping a 3-way and so on.

Speakers that feature a high pass filter or low pass filter will usually either have a pre-determined cutoff frequency, or have a choice of two or three user-defined selections. These filters are used to adjust the speaker’s frequency range to suit different room acoustics, or to raise the low-end cutoff when used with a subwoofer in a 2.1 or surround-sound setup.

This is the measurement which people often get a bit over-excited by and is also the figure which is most frequently misinterpreted. The power rating alone doesn’t tell you how loud your speakers will go - other specifications such as the sensitivity and impedance of a speaker all make a difference to the actual volume that it can achieve, not to mention how liberal the manufacturer is with their specifications! The power rating is measured in Watts and can be described as ‘RMS’, ‘program’ or ‘peak power’. As mentioned in the text above, it is now most common to match the RMS rating of an amplifier with the program rating of a speaker. Peak power can have so many different meanings that it is best avoided altogether.

The term SPL is an abbreviation of ‘Sound Pressure Level’, and as with power rating it is a measurement that can be confusing as it is commonly presented in several different ways. The basic measurement involves playing a sine wave through the monitor with an SPL meter positioned at a set distance - usually one metre. As all manufacturers measure this specification differently though in terms of how long the measurement is taken over, at what frequency and at what level of acceptable distortion, it is very difficult to use this figure for accurate comparison. There currently being no industry standard, manufacturers often use this vagueness to their advantage, calculating impressive ‘on spec sheet’ results, with some even providing purely theoretical figures based on the speaker’s design characteristics.

Frequency response is a measurement of the range of frequencies a speaker can reproduce. Although there are a multitude of theories concerning the range of human hearing, it is most commonly defined as ranging from 20Hz to 20,000Hz (20kHz). Most modern speakers extend up to 20kHz at the top end, but smaller enclosures can find it difficult to reproduce lower frequencies, with many ‘cutting off’ at around 60Hz. These frequencies are particularly important to producers of some genres of music, dance in particular, and anyone involved in mastering should have speakers capable of reproducing these frequencies. Those with smaller monitors may want to supplement the low frequency response of their near-fields with a separate subwoofer. As with all specifications, the devil is in the detail, and it’s important to compare like with like. The most common definition of the upper and lower limits of frequency response are the points where it starts to drop by 3dB or more – figures without a definition of the ‘cutoff’ point are meaningless!

Woofers are designed to reproduce bass frequencies, whereas tweeters are specifically for high frequencies - a crossover is therefore required to send the relevant frequencies to the separate drivers. The crossover frequency is the frequency at which the audio signal is divided.

Measured in Ohms, impedance is the combination of the electrical resistance of a speaker and its ‘reactance’. This figure is not as important as it once was due to the prevalence of powered and active designs, but is vital when matching amps and speakers, particularly when connecting a number of speakers together such as in a PA system. Most single speakers are now rated at either 4 or 8 Ohms, and most modern amplifiers are capable of driving a variety of different impedances.

The merging and editing of individual audio signals (band, sequenced tracks, microphone etc.) to create a single stereo or surround sound recording. For mixing you need a mixer, effects device (unless the mixer has an integrated one) a stereo amp and if possilbe good studio monitors.

Mixing is just as artistic and creative as the composition and interpretation of music, if not the most important step in the process of digital music creation. In the audio industry the audio engineers are just as famous as the stars which they help rise to fame.

Depending on the material of the absorber (carpet, curtain, foam board) and the texture of the surface, different frequencies will be absorbed. Nowadays every application has an appropriate absorber solution to optimize the sound in the studio, listening or demo room being used. So it's best to get advice on the best solution for your space from someone with experience!

In acoustics: determines the size of the vibration (it's range), the bigger it is the louder the volume will be.

It is the optimization of the signal level for sound recordings. If the levels are too high it causes distortion. In analog recording this is, to a certain extent, acceptable and sometimes deliberately produced but it is catastrophic for digital recordings. If it is too low the signal to noise ratio degrades.

It is the area between the highest and lowest frequency at which an audio system can operate. The optimal frequency is between 20Hz and 20kHz for the hearing of a young person which is why most audio systems operate there. It is important however that the frequence response be as linear as possible.

A speaker box with a bass reflex has an opening on the front which allows low-frequency vibrations, that would otherwise be absorbed by the box itself, to be emitted to the outside. Bass reflex boxes have a higher efficiency than normal speakers at low frequencies because of this.

Refers to the process of attenuating the sound (in a room for example) through various measures such as increasing the air resistance (foam insulation on the walls).

In a room diffusion is created through the reflection of sound which gives us the perception of space. In programmable reverb devices and room simulators the diffusion can be controlled separately most of the time.

The dreaded effect of an overdriven recording: distorted level peaks make a sound recording useless in most cases.

The range, usually expressed in dB, between the softest and loudest sound a device can handle. The usable range of the sound is found where there is a nominal level and inherent noise. If a signal source fluctuates too much in its 'loudness' it is referred to as having a high dynamic range. The human voice for instance has a high dynamic range, every word in a sentence can have a different volume. Compressors make sure that these volume differences are 'compressed', reducing the dynamic range and bringing the volume to uniform level. The human ear can tolerate a maximum dynamic range of about 130 dB before reaching the pain threshold. Analog tape recorders achieve a dynamic range of 60 to 80 dB (without Dolby or dbx). Digital systems can achieve over 100 dB of dynamic range.

The amount of sound that directly reaches the listener or microphone (as opposed to the sounds that are disturbed or reflected). For clear voice recordings, direct sound is particularly important.

The dynamic bandwidth of an audio system, shown in decibels, represents the difference between the minimum and maximum output volumes achievable without distortion. The larger the bandwidth the more faithful the sound repoduction will be. As for a single instrument, it is the bandwidth from the loudest to the quietest sound of the instrument.

This term refers to the conversion of sound into electrical vibrations and vice versa. They term came in to existence with the invention of the electron tube (about 1930) for amplification and generation of vibrations. Despite increasing digitization, microphones, amplifiers and loudspeakers remain the basic elements of electro acoustics.

It is the last link in the audio chain before the speakers. Most of the non-controllable amps deliver the required signal to the speakers after it has been brought to the appropriate level by a pre-amp in the form of a mixer. These days power-amps are being built into the speakers themselves which has the advantage of ensuring they are optimized for one another. In hi-fi systems the stereo power-amp is usually housed in the central unit, while high end public address systems have separate power amplifiers, which is advantageous because of the enormous heat created and possible transformer interference.

A special filter where the frequency band is, for the most part, freely adjustable. A graphic equalizer allows you to adjust specific frequencies based on presets built into the EQ but doing so affects the other frequencies as well. In contrast, a parametric EQ allow you to adjust aspects of each invidual frequency as well as allowing you to choose which one exactly you are adjusting.

A way to cahnge the frequency response in order to produce the desired sound. A low pass filter lets the lows pass, a high pass lets the highs pass, and a band pass grabs frequency band from the middle and cuts off the highs and lows.

Passive filters can only dampen frequencies (which causes other frequencies to come through stronger) while active filters can usually amplify them as well. One of the most well known active filters is the equalizer which is mainly used in sound processing. An important aspect of a filter is the cut off frequency, this determines at which frequency the filter will being taking effect.

It is the term for the number of full oscillations (= oscillation periods) in one second. The frequency of a tone is responsible for the pitch (perceived by the human ear) and the unit used to measure them is a Hertz (Hz). Doubling the frequency results in an octave increase in tone, for example if a = 440 Hz then a'= 880 Hz and a'' = 1760 Hz, etc. Most people can hear sounds in the range between 30 Hz and 16 kH. When AC voltage in a loudspeaker is converted into air pressure fluctuations, it becomes an audible sound.

Human hearing has the ability to perceive frequencies between 20Hz and 20Hz. However this is only possible for a small group of young people. In part due to the damage caused by everyday noise levels as well as (voluntary) damage caused by things like listening to music too loud, which can lead to a rapid decrease in hearing. In addition, the ability to perceive the higher frequencies simply decreases as we get older.

They are a type of speaker specially designed to produce higher frequencies. Tweeters can be found in a variety of designs and badwidths in combination with normal speakers or as separate satellite boxes.

For speakers: It refers to the ability to reproduce short signal peaks. Since this depends on the design of the membrane and is adversely affected by their inertia, a good impulse response gives at least a clue about the playback quality of the speaker.

They are constructed to convert electrical waves into acoustic/sound waves. The electrical waves contact the speaker via a magnet and the alternating polarity of the magnet causes a membrane to oscillate, which then causes the surrounding air to resonate. These resonations are in turn what causes audible sound to come from the speaker. Speakers can only play a certain frequency range and are separated into bass, midrange and tweeter speakers.

A sort of automatic volume control: When the input signal is to high the limiter adjusts the gain automatically to the required level. A limiter prevents accidental overloading of subsequent devices but can cause some annoying side effects like hissing or ticking. A limiter has the same parameters as a compressor but allows much higher ratio settings of 10:1 to 20:1.

If all tracks are recorded and ready for playback then they can be combined in the ''mix''. Each track has its own EQ, volume, and effects settings.

They are studio monitors which are designed to produce, through their sound radiation, the correct frequency response at a 1-2 meter distance. Theoretically this mitigates the need for proper room acoustics.

The time difference between two oscillations or their zero crossings is referred to as phase shift. This allows positive and negative half-waves to meet. Since these can cancel each other out, it can lead to level losses and, in extreme cases, the signals cancel out entirely. You should always pay attention to your mixes and make sure they play well in mono, as this is where the effects of the shift will come through most. So always reset the mixer to mono after shifting and listen to your sound.

Air movements emanating from sounding bodies which are perceived as sounds.

It causes all tones over an appointed frequency, the cut-off frequency, to be filtered out. Allowing only the low tones to come through.

Speakers which are specially designed for the conversion of low frequency audio signals. Subwoofers are produced in different styles and bandwidths in loud speaker combinations or as separate subwoofer boxes.

After the completion of a ‘mix’ (see mixdown) all the compositions need to be made ready for production (e.g. made into CD’s or released as digital albums). This is the point where the volume levels of the individual tracks are normalized, the cleanness of the phase correlation (mono compatibility) of the entire recording is checked and, where possible, optimized by adjusting the sound behavior and dynamics of the individual pieces. The order of the tracks, the pauses between them, and their ID’s are finalized, essentially putting the final touches on the album or composition as a whole.

Mastering can also refer to the editing of a mix on an individual track without relation to other tracks. The sound characteristics are assessed again and small changes may be made. But it is no longer possible to process individual sounds as in the mix at this stage, rather individual frequency bands can be edited with equalizers and multiband compressors.

Pre-production refers to a first simple (demo) production of a song, which is usually also used as a guideline in the actual production. In some cases, the individual elements of the pre-production track are used as a base for individual (basic) tracks in the final production. Usually the intent is that they will be replaced by the final takes, if however the pre-production goes well enough, or has a unique character, it may be that parts of it are used in the finished production as well.