Pad

An electronic circuit designed to attenuate the output of a device by a given amount. For example, some microphones have so much output that they can overdrive the input stage of many mic preamps. To prevent this, mic designers will include a switchable "pad" on the output stage of the mic, attenuating, or reducing the mic's output by 10 or 20 dB. While many devices have built-in pads, it is also possible to purchase external pads, which plug in to a device's output and reduce its level.
A sustainy, "wash" or fill sound, usually used as harmonic background material in a musical arrangement. Arrangers often speak of using a "string pad" during a passage; this would be a section of strings playing long, sustained chords behind the melody. With the advent of samplers and synthesizers, other types of sounds have also become common as pads; just about any sound that can sustain can be used as a pad these days!

Pancake

Not the breakfast food. In audio, pancake is slang for a reel of recording tape without the actual reel flanges. In other words, it is simply the tape wound onto a hub with no side supports. Recording studios often buy tape in this form because it costs less due to the expense of the reels. To use it a studio will either spool tape off of it onto other reels or swap the actual reels from another reel of tape.

Panic Button

Once in a while a problem occurs in a MIDI system, and when it does one of the symptoms is quite often stuck notes that continue ringing or continuous controllers that no longer operate correctly. Some devices, especially MIDI patch bays or MIDI interfaces, have a panic button to solve this by sending All-Notes-Off and Reset-All-Controllers commands. Some software programs also have a command that performs this function. While not correcting the problem that caused the malfunction a panic button is a great way to get the system quiet and to get the equipment into a state where it can reliably receive more MIDI messages.

Parametric Equalizer

A type of equalizer having several "parameters" for control of various filters that can be applied to audio signals. Parametric equalizers are most widely used in situations where very fine control over the audio signal is desired. In order for an equalizer to be parametric it must at least have control over gain, Q, and frequency. In most cases each of these controls are on rotary potentiometers, but there are a few graphic style parametric equalizers on the market. Some equalizers have selectable frequencies that can be adjusted, but no Q control. These are known as quasi-parametric or sweepable equalizers.

Passband

A term used when working with filters. Passband refers to the frequency span (range) a filter passes, or the range of frequencies not attenuated by a filter. The passband is usually measured between the points where the response is 3 dB down in amplitude relative to the maximum overall level.

Passive

A passive audio device is one which does not use amplification circuits. By nature of design, passive devices do cause a loss in power (insertion loss). Because they do not contain amplifiers, and are "cut-only" or "subtractive" in operation, passive devices tend to not add noise or distortion to a signal (although noise may be added in compensating for insertion loss). Typical passive devices include direct boxes, splitters, equalizers and crossovers.

Patch Mapping

A function of some MIDI devices, patch mapping allows an incoming MIDI Program Change message to be assigned to call up any of the receiving device's internal program numbers. For example, an incoming MIDI Program Change message with a value of 44 might be mapped to call up internal program number 95, MIDI Program number 67 might call up internal program number 14, and so on. There are a variety of reasons for using this function. Just a few:

When layering sounds in a live situation, a single program change message from a controller can simultaneously call up several sounds located in different MIDI modules at different patch numbers.
On devices which have more than 128 patch locations, but don't respond to bank select messages, internal programs higher than #128 can be accessed using mapping (E-mu's Proteus family comes to mind as one example).
The most basic reason: convenience! Rather than copying patches around to put them in the order you want or need, simply use patch mapping to establish the desired order, and call them up through MIDI.

PCI (Peripheral Component Interconnect)

A high-performance (by current standards) computer expansion slot designed by Intel. PCI allows for 32- or 64-bit bus specification. PCI is described as high-bandwidth and processor-independent data path between the CPU and high-speed peripherals. The PCI spec allows for the capability to transfer up to 132 megabytes per second at a bus clock speed of 33 MHz (although the current rates being claimed by manufacturers are more commonly in the 30 Mb/sec range). This speed makes it especially suitable for high data rate applications like digital audio and video. PCI slots are found in the current generations of both PC and Macintosh personal computers.

PCM Deck

PCM (see WFTD archive Pulse Code Modulation) commonly refers to digital recorders that use videotapes as the recording media, even though Pulse Code Modulation is the process by which digital data is encoded on most all types of digital recorders and CDs. This is mostly because the first decks that could handle the wide bandwidth of PCM data were video decks, and some (namely Sony's) had PCM as part of their model names. After converting the analog signal to digital data, it is converted to a composite video signal compatible with video cassette recorders and sent to a video deck. Usually these signals were recorded on VHS or beta at the semi-pro end of things, though Beta had been more preferred for PCM because it tracked better than early VHS decks. At the pro end a U-Matic (3/4") VCR or a 1630 PCM machine were used.

Most dedicated PCM machines and converters are old, bulky, and have been all but discontinued. They are still the preferred format by many pros, however, and most compact discs are mastered on the Sony PCM 1630, a $30,000 reference standard.

PD Drive

Developed by Panasonic, PD is a new type of removable media drive that combines an optical disk drive with a quad speed CD reader, essentially giving you two drives in one. A PD drive alternately accepts standard CDs and PD rewritable optical disks into a front loading tray. When the media is inserted into the drive, a micro-optical head inside the PD drive automatically senses which type of media has been inserted.

PD media is a new form of optical disk, which uses a 120mm diameter, single-sided, phase change disk enclosed in a protective cartridge storing up to 650MB of data. The drive can read, write, and erase the PD media.

Peak Hold

On non-mechanical (LED) indicators, Peak Hold allows the meter to continue displaying the highest signal level for a certain amount of time or until it is exceeded by an even higher peak. This is very useful, as it gives clear indications of where and how hot peaks are, but still allows monitoring of the current signal level. Knowing where the peaks are allows easier adjustment of dynamics processing, as well as more accurate input and output level settings on other gear.

Peak Program Meter (PPM)

An alternative to VU meters (see WFTD archives "VU Meter"), Peak Program Meters have fast rise times (30 times faster than VU meters) and a much slower fallback or decay time. Peak Program Meters respond to peak levels rather than average levels. This makes them especially useful in situations where distortion or overload is a significant concern, as in digital applications. Because other meters, (i.e. VU meters) respond more slowly, giving an average level reading, they are not as useful for indicating maximum levels or peaks. Popular in Europe, PPMs are found in mechanical, LED, and/or plasma forms in a variety of equipment types.

Phantom Power

A DC (direct current) voltage, usually 48 volts, applied across pins 2 (+) and 3 (-) of an XLR microphone connector that can be used to power transducers with active electronics. Condenser microphones require a pre amp close to the very high impedance (See WFTD archive "impedance") diaphragm which requires power to operate. Back in the '50's and '60's this power was often provided by a separate power supply that came with the microphone. Later manufacturers began to provide a source for this power at the microphone input to mixers or pre amps. Since the power is carried on the same wires that carry the audio signal, and since most dynamic microphones and other passive devices are not affected by this DC voltage it was known as "phantom" power. The theory was that only devices that needed it would be wired in such a way that they would use it. Nowadays almost all condenser microphones and active direct boxes are able to use phantom power when it is present on a microphone cable. Consequently most mixing board manufacturers include this feature in their products.

Phase

Audio waveforms are cyclical; that is, they proceed through regular cycles or repetitions. Phase is defined as how far along its cycle a given waveform is. The measurement of phase is given in degrees, with 360 degrees being one complete cycle. One concern with phase becomes apparent when mixing together two waveforms. If these waveform are "out of phase", or delayed with respect to one another, there will be some cancellation in the resulting audio. This often produces what is described as a "hollow" sound. How much cancellation, and which frequencies it occurs at depends on the waveforms involved, and how far out of phase they are (two identical waveforms, 180 degrees out of phase, will cancel completely).

Phase Invert

A switch found in the input sections of mixing consoles and mic preamps. The term "phase invert" is actually a misnomer, since what the switch really does is invert the polarity of the signal in that input (correct usage would be "polarity invert"). Its intended use is to correct for balanced lines and mics that are wired backwards. In some cases toggling the phase invert switch may make a sonic difference if signals are out of phase, but doing so will also put that signal out of polarity with the others. (See also WFTD "Phase" and "Polarity")

Physical Modeling Synthesis

A type of sound synthesis performed by computer models of instruments. These models are sets of complex equations that describe the physical properties of an instrument (such as the shape of the bell and the density of the material) and the way a musician interacts with it (blow, pluck, or hit, for example).

Pigtail

In audio (as opposed to butchery) a pigtail is the end of an audio cable which simply has bare wires rather than any type of connector. Pigtails are used to connect wires to binding posts and screw terminals.

Pink Noise

Random noise with equal energy per octave. Our ears perceive this as sounding relatively "flat" in frequency response (since pink noise is based on octaves rather than individual frequencies, there is no increase in energy in the high octaves). Because of this, and because Real Time Analyzers (RTA) tend to look at octave or 1/3 octave ranges, pink noise is very useful for measuring the frequency response of audio equipment, as well as for determining room response for sound reinforcement applications.

Play List

Often written as playlist (one word), the term has come into use with hard disk recording systems. It refers to a list, or some sort of view of audio items that can be defined to play in a particular order (usually the order shown in the list). One track of Pro Tools (or almost any digital audio program) can be thought of as a play list. The shown audio regions will play back in order, even though they may have nothing to do with one another. Though the term is used more loosely like that these days, it originates with early disk recording systems that simply showed the sound files in text form in the order they were to be played. One of the earliest of these, Digidesign's Sound Designer, was very popular with rap and R & B artists for making dance edits of their tunes. Though we have progressed quite a bit since then, some relatively high-end systems still use a play list style of editing to this day. And there are people who still swear by Sound Designer for the ease of use in doing this type of editing.

Plosive

A phenomenon that occurs when humans speak words that require a complete closure of the oral passage followed by the release of a burst of air. This commonly occurs in everyday speaking. Sounds like the "P" in the word "pit" or the "D" in "dog" will produce a sudden burst of air from the mouth. If you place your hand in front of your mouth and make these sounds you will feel the burst of air. These sudden movements of air can be a real problem for sensitive microphones recording vocals. To a microphone this mammoth air movement will sound like a loud, bassy pop or thumping sound. Pop filters are commonly used in recording sessions to reduce this problem.

Polarity

In electronics, two points that have opposite electric potentials (one is positive, the other negative). This is not the same as being 180 degrees out of phase (although the results can be similar). Phase implies a relationship with time, polarity does not. What most engineers, consoles and preamps refer to as a "phase" switch is actually a switch reversing signal polarity.

Polarity is important when interfacing equipment, particularly speakers - you don't want one cone moving in while the other moves out. Some designers feel that maintaining "absolute polarity" (no polarity reversal in a signal chain) throughout a signal path is important.

While tests don't indicate that the ear can hear which polarity is correct, they do show that it may be possible to detect a difference between normal and inverted polarity signals. (Try it for yourself in a critical listening environment: Play a signal though a single speaker, then reverse the speaker wires and play the same signal again - remember to switch the wires back when you are finished!)

Polar Pattern

Depending on their design and construction, microphones respond to sound coming from different directions with varying degrees of sensitivity. A plot or graph of this response is called a polar pattern (sometimes polar response curve). Looking at a mic's polar pattern will tell you how directional it is, how well it will reject sound from certain directions, etc. It is important to note that polar patterns are frequency dependent. Typically, low frequency response will be almost omnidirectional; the polar pattern will be come more directional as frequency rises.

Pole Piece

A shaped piece of high permeability metal, usually soft iron, which serves to concentrate and direct the magnetic field of a permanent magnet to maximize efficiency of devices like loudspeakers, magnetic cartridges, and cutterheads. Pole pieces are needed because magnets are hard (expensive) to make in the complex shapes that can be needed. In layman's terms, the Pole Piece is the part of the speaker magnet assembly that the voice coil (see WFTD archive voice coil) slips over. It is the center round piece.

Polyphonic

When discussing musical instruments, the ability to play more than one note simultaneously. All instruments have a finite number of notes they can produce at one time. For example, a six string guitar has a maximum of 6-note polyphony. A synthesizer might be 32-note polyphonic, and so on. The more notes of polyphony an instrument can produce, the more capable it is of playing complex arrangements and chords. If the polyphony of the instrument is exceeded, it must "steal" the notes it needs from others that are already sounding. For example, a synthesizer might steal the last note requested from the first one hit; the first note stops, and the new one begins to sound. Some synths and samplers use sophisticated algorithms for voice stealing, others allow you to pre-allocate a given number of voices to a particular MIDI channel, and so on. Compare "polyphonic" to "multitimbral" in the WFTD archive.

Pop

A bassy thump or "explosive" sound heard in a vocal mic (this is called a "plosive"). Pops often occur when the vocalist pronounces words with "p", "t", "b", etc. sounds in them. These consonants can create a puff of air that strikes the microphone diaphragm, creating a thump in the audio signal. In general, windscreens will help with pops to an extent, but a pop filter will be more effective. Be careful that the pop filter you choose is transondent (see WFTD archive), and serves only to break up the plosive's effects.

Pop Filter

A pop filter is used with microphones to shield the diaphragm from sudden bursts of sound which can cause a popping (see WFTD archive "pop") effect. The shield is transondent (see WFTD archive "transondent") and does not interfere with the movement of sound towards the microphone. Pop filters, which usually look like a 6" to 8" circle of mesh material, are commonly seen in recording studios situated between 1" and 8" in front of a microphone.

Potentiometer

An electronic component that used to provide variable control over an electronic circuit. Usually controlled by a rotary knob which can be turned by hand, a volume control is a good example of this. A potentiometer is often called a pot for short.

Power Supply

A subsystem of virtually every electronic device that takes the electrical service power and converts it into some form(s) that can be used to properly power a given device. This may include turning the AC current into DC, known as rectifying (most electronic equipment uses DC power to operate), stepping down the voltage to something more suitable for low power electronic devices, and filtration to make sure they have clean power to work with. At times the voltage may be stepped up for devices that use high voltage tubes. Regardless of the specifics the overall job of the power supply is to provide good, clean power for the device.

They tend to be overlooked because of their ubiquitous nature, but the power supply is a very critical and often expensive component that can make or break a piece of audio gear. While their function, officially, is to just supply power, we must remember that this power can and will affect the way the device in question operates. Feed it dirty, unstable power and you'll get commensurate results. "Wall Wart" and "Lump in the Line" type supplies have become popular in recent years because they are inexpensive to build and can be used on a wide variety of devices. These are generally fine for low power equipment (especially if more filtering is employed inside the device), but most high-end pro audio equipment will have an internal supply that is optimized for it.

PPQN (Pulses Per Quarter Note, sometimes Parts Per Quarter Note)

The timing resolution of a MIDI sequencer. PPQN indicates the number of divisions a quarter note has been split into, and directly relates to the ability of the sequencer to accurately represent fine rhythmic variations in a performance, or to recreate the "feel" of a performance. Older sequencers were capable of 96 PPQN (sometimes even less), which often resulted in a stiff "quantized" feel to the music (even if it hadn't actually been quantized). Current versions can reach 768 PPQN or even higher resolutions, which is more than adequate for most musical applications. Note that the resolution of the sequencer is especially important at slower tempos. If your sequencer is limited to a lower resolution, one trick is the double the tempo of the song, then perform the parts in half time. This effectively results in a doubling of resolution.

Pre-delay

Pre-delay is a parameter found in reverb processors. It refers to the amount of time between the original dry sound, and the audible onset of early reflections and reverb tail. Carefully adjusting the pre-delay parameter makes a huge difference in the "clarity" of a mix. For example, a longer pre-delay will move the reverb tail out of the way of the vocals, making them much more present and understandable.

Pre-Fade Listen (PFL)

In a console, pre-fade listen is a one of several possible means of overriding the normal monitor signal routing for various purposes. PFL generally sends a signal to monitor outputs regardless of the setting of that channel's fader, and simultaneously mutes the other channels. In other words, PFL allows you to solo a channel even if the fader is pulled all the way down. Note that on most consoles, this affects monitors only, and does not interfere with main, tape, or aux outs. In broadcast situations, PFL is often referred to as "cueing".

Pressure-gradient Microphone

A microphone in which both sides of the diaphragm are exposed to the incident sound. The microphone is therefore responsive to the pressure differential (gradient) between the two sides of the membrane. Sound waves parallel to the plane of the diaphragm produces no pressure differential, and so pressure-gradient microphones have figure-eight directional characteristics. These are also sometimes called "velocity microphones", since the output voltage is proportional to the air particle velocity.

Pressure Microphone

A microphone in which only one side of the diaphragm is exposed to the impinging sound. The diaphragm responds to the pressure variations uniformly and therefore pressure microphones are inherently omnidirectional. Also sometimes called "pressure operative microphone".

Pressure Wave

This term is not as scientifically grounded as it is descriptive, but we do hear it used to describe sound propagation quite a bit. When a sound first occurs there is always an initial wavefront or pressure that is generated in the air. Changing air pressure is how sound is heard by the ear and also how sound is able to move through the air. There are waves of high and low pressure that correspond to the frequency(s) and volume of the sound. The phrase "pressure wave" is usually used to describe the "initial" high pressure zone created by the onset of some sound. For example: If a drummer hits a drum, the movement of the drum head when first struck creates an area of high pressure around the drum that then moves the surrounding air molecules, and so on until it reaches the ear. This is the initial pressure wave. It is followed by other waves of higher and lower pressure that correspond to the sound of the drum.

Program Change

Also known as Patch Change, a type of MIDI message used for sending data to devices to cause them to change to a new program. Program Changes messages are channelized so they will only affect a device on a specific MIDI channel. These commands are used in all sorts of MIDI applications ranging from simply changing patches on a synth or reverb to controlling lighting systems. Software sequencers that appear to have the programs of your keyboard in them by name are in fact using program change commands that are known to pull up those programs in your keyboard.

Proprietary

This is a word that is (unfortunately) used fairly frequently in the computer and audio worlds. In the broader sense, proprietary means that a concept or product is unique to, and the property of a manufacturer or company. More commonly, proprietary refers to a manufacturer designing a product to only work with other products from that same manufacturer. For example, a manufacturer might make a synthesizer that can only save patch information to specific, specially designed RAM cards, rather than to more universal PCMCIA cards, floppy disks, or whatever. In order to save that synth's information you would be required to use the proprietary cards available only from that manufacturer. While the word "proprietary" is often given a negative connotation, keep in mind that building gear around proprietary designs and options allows a manufacturer to implement features that might not be possible if everything were standardized and generic.

Proximity Effect

An increase in bass or low frequency response when a sound source is close to a microphone. Proximity effect is distortion caused by the use of ports to create directional polar pickup patterns, so omni-directional mics are not affected. Depending on the mic design, proximity effect may easily result in a boost of up to 16 dB, usually focused below 100 Hz. Vocalists tend to like proximity effect since it fattens up their voice, but a constantly varying bass boost can wreak havoc on headroom and carefully set levels! Obviously, if a vocalist is "eating the mic" to get proximity effect, the Inverse Square Law (WFTD 6/12) tells us that the levels the mic sees are increasing dramatically as well - distortion can easily result, from either mic diaphragm breakup or electronic overload. (You may occasionally see proximity effect referred to as "bass tip-up")

Pull Down

Pull Down is a phrase that can have two meanings in audio/video production depending upon the context. There is the NTSC Pull Down that we will discuss here, but there is also something known as 3/2 Pull Down that pertains to telecine transfer of film to video (which we will cover later). NTSC Pull Down (also written as pulldown) refers to a .1% slowdown which occurs when elements that are created to a 60 Hz reference, such as film and location sound, are later referenced (synchronized) to the 59.94 Hz NTSC (Black Burst) reference. In the case of 30 FPS (Frame Per Second) time coded materials, they are pulled down to 29.97 FPS.

3/2 Pull Down

Another of those dreaded sync terms. One of two types of pull down pertinent to synchronization, and guess what? The two get confused quite often. We've already discussed what Pull Down is (see WFTD Pull Down). 3/2 pull down is a specific type of pull down employed when film is transferred to video tape. The problem is that film is generally shot at 24 FPS (Frames Per Second) and video in the United States is generally around 30 FPS. It is desirable to have each film frame correspond to a video frame, but because they operate at different frame rates this is impossible. It is also not acceptable to speed up the film to video's 30 FPS during transfer to video (unless it's one of those old Charlie Chaplain movies). The best compromise has been to employ 3/2 pull down during the telecine transfer, which reconciles the 24 FPS of film with the 30 FPS of NTSC video by scanning in the second field of video twice on every other frame of film. This effectively creates an extra 25% of visual filler to occupy the six extra frames of video that occur each second. Amazingly this process is pretty much undetectable to those who aren't looking for it and is the way film has been transferred to video for many years now.

Pulse Code Modulation (PCM)

A method of encoding and de-encoding a digital signal. There are actually several varieties in use today, including linear, non-linear, floating point, and differential. These vary mainly in how they deal with quantization, and how they handle values that fall "between" the digital signals bits.

Punch Block

A type of terminal strip, first used by the telephone companies. It uses small, metal, V-shaped terminals into which wire is pressed with a special tool (which is called, amazingly, a "punch-down tool"). The V-shaped groove cuts through the wire insulation to make contact with the wire so that no soldering or stripping is required.

Push-Pull

A type of amplifier design. Push-Pull is a term that originated in the days of tube amplifiers (which are now having a resurgence). In this design two output tubes are connected in such a way that while the current in one is increasing, it is decreasing in the other. The two signals are then combined in an output transformer and passed on to the load (speakers). The modern solid-state version of this is known as the Complementary Symmetry Circuit (though most lay people still call it push-pull), where two transistors operate in a similar fashion. There are several classes of operation of push-pull designs that we will discuss in upcoming weeks.

PZM

Many of our recent Piano Miking Suggestions recommended use of PZM microphones. PZM (Pressure Zone Microphone), or more correctly boundary mics (PZM is a trademarked term) use a small electret capsule mounted close to a backing plate. The idea is that the mic capsule/plate is mounted to a large flat surface (or boundary). This increases the sensitivity of the mic by 6 dB (due to pressure doubling from reflected soundwaves), and gives it a hemispherical pickup pattern. The practical frequency response of the mic will depend on the size of the flat surface it is mounted to. If the surface is too small, low frequencies will not be reflected resulting in an apparent high frequency (treble) boost.