Pro Audio Reference


Pro Audio Reference (Numbers)


0 See zero.

0 dBFS See decibel.

0 dBm See decibel.

0 dBr See decibel.

0 dB-SPL See decibel.

0 dBu See decibel.

0 dBV See decibel.

1/3-octave See one-third octave.

1/4" TRS or 1/4" TS See connectors.

1 The other half of all the stored knowledge in a computer; compare with zero. And, surprisingly, not a prime number. A prime number is defined to be a natural number (i.e., a positive whole number) greater than one which has exactly two different factors: one and itself.

1/f noise See flicker noise.

1T DRAM A one-transistor dynamic random access memory design that significantly reduces the area required for a single memory cell. This capacitor-less design works by storing a binary 1 as excess positive charge in the device body and a binary 0 as excess negative charge. First described by Pierre C. Fazan and Serguei Okhonin, Mikhail Naggoga and Jean-Michel Sallese in their paper, "A Simple 1-Transistor Capacitor-Less Memory Cell for High-Performance DRAMS."

3 The number of seconds it takes a bluefin tuna or a Porsche 911 GT3 to go from 0 to 50 mph.

3D See 3D sound.

3-dB down point or -3 dB point See passband.

3-to-1 rule Microphones. The rule for spacing multiple microphones, which says that the distance between them should be at least three times the distance from each microphone to its source. [Vear] For example, if the microphones are placed one foot from their source then they should be spaced three feet apart. This reduces phase cancellations between adjacent microphones.

4 The only number that equals the letters in its name: four.

+4 dBu See decibel.

4 Elements see: Four Elements.

4 x 4 x 8 feet A cord of wood (128 cubic feet or 3.62 cubic meters). Not to be confused with chord.

4-wire See Kelvin connection.

5.1 See 5.1 surround sound.

6.1 Extended version of 5.1 surround sound called Dolby Digital EX (previously Dolby Digital ES) where one rear center channel is added to the basic 5.1 group resulting in: left-front, center, right-front, left-surround, right-surround, rear and subwoofer.

6s or 6 Sigma See Six Sigma.

7.1 Extended version of 5.1 surround sound with Dolby True HD, Dolby Digital Plus and Dolby Pro Logic IIx where left and right rear channels are added to the basic 5.1 group resulting in: left-front, center, right-front, left-surround, right-surround, left-rear, right-rear and subwoofer.

8 nickels = 2 paradigms.

8Stem An "... interactive audio format that allows any listener to remix music like a professional DJ or sound engineer." [from website] Developed by a Seattle company.


8-Track Recording. A popular, albeit short life span, analog tape format invented and patented by William Powell Lear, founder of Learjet, in 1963. See: Lear cartridge. Also see: Eight Track Museum.

9 Greek Mythology. The number of muses: Clio (history), Melpomene (tragedy), Thalia (comedy), Calliope (epic poetry), Urania (astronomy), Euterpe (flutes & music), Terpsichore (dancing and lyric poetry), Polyhymnia (mime and sacred poetry), and Erato (love poetry).

10Base-T or 100Base-T or 1000Base-T or 1000Base-F See Ethernet.

10 billion The number of mathematical calculations required for a one-day weather forecast. (Snapple Real Fact #65)

-10 dBV See decibel.

10-string double violin Listen to L. Shankar playing here. His niece, Gingger Shankar, is the only women known to play this instrument.

10.2 Somewhat tongue-in-check term created by Tom Holman (of THX fame) for his experimental (but impressive) surround system based on 5.1 surround sound, but with twelve channels.

11 Mythical nirvana position of the amplifier volume knob for Heavy Metal rockers, first made famous by the movie “This is Spinal Tap.” Here is the movie dialog:

Nigel Tufnel: The numbers all go to eleven. Look, right across the board, eleven, eleven, eleven and ...
Marty DiBergi: Oh, I see. And most amps go up to ten?
Nigel Tufnel: Exactly.
Marty DiBergi: Does that mean it's louder? Is it any louder?
Nigel Tufnel: Well, it's one louder, isn't it? It's not ten. You see, most blokes, you know, will be playing at ten. You're on ten here, all the way up, all the way up, all the way up, you're on ten on your guitar. Where can you go from there? Where?
Marty DiBergi: I don't know.
Nigel Tufnel: Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?
Marty DiBergi: Put it up to eleven.
Nigel Tufnel: Eleven. Exactly. One louder.
Marty DiBergi: Why don't you just make ten louder and make ten be the top number and make that a little louder?
Nigel Tufnel: [pause] These go to eleven.

12:00 Syndrome The phenomenon affecting too many pro audio sound people whereby they feel obligated to set all rotary controls "straight up," or within an 11:00 to 1:00 aperture, thereby destroying all the product designer's good work to provide them with a large range of adjustment to cover contingencies.

16 2/3 rpm Phonograph recording speed obtained using a half-speed converter on a 33 1/3 rpm machine, used for special recording purposes, but never a standard. However, used in 1956-1959 Chrysler Imperials. See: HighWay Hi-Fi. [Thanks, Bink!] See Record Speeds.

19 The number of electronic music genres cataloged.

24 The number of hours in a day. From Otto Neugebauer's, The Exact Sciences in Antiquity:

"A second Egyptian contribution to astronomy is the division of the day into 24 hours, though these hours were originally not of even length but were dependent upon the seasons." A little further on he says, "Thus our present division of the day into 24 hours of 60 minutes each is the result of a Hellenistic (Greek) modification of an Egyptian practice combined with Babylonian numerical procedures."

[Ah, but why you ask; why not some other number? See 60 for more on the Babylonian (Sumerians) numerical procedures.]

24/96 Data conversion using 24-bits quantization at 96 kHz sampling rate.

24/192 Data conversion using 24-bits quantization at 192 kHz sampling rate.

25 (sometimes 24) See: quire.

25 or 6 to 4 Song title appearing in 1970 on Chicago II, written by organist/vocalist Robert Lamm. In spite of all the urban legends to the contrary, the title is a reference to the time of day, i.e., "25 or (2)6 minutes to 4 a.m." according to writer Robert Lamm. See The Straight Dope for the interesting details.

33 1/3 rpm record The standardized phonograph recording speed selected for the long-play record. Warren Rex Isom explains the reasons in his article, "Before the Fine Groove and Stereo Record and Other Innovations," published in the Journal of the Audio Engineering Society, October/November, 1977, Vol. 25, No. 10/11, pp. 815-820. The quick answer is that Western Electric synchronized motion pictures with phonograph records in 1925. A reel of 35-mm film runs for 11 minutes. A record needed to play the same length of time, which was 3.66 times longer than the 3-minute 10-inch 78-rpm standard. After considering optimum needle groove velocity and diameter, while shooting for something approximately half of the 78-rpm standard that would easily lock to the 60 Hz line, 33 1/3 rpm was the answer arrived at by Maxfield (see Isom for the exact details). See Record Speeds.

33/45/78 If you were born in '33, you would be 45 in '78. [Thanks to JR at the BBC for this one.]

42V PowerNet See 42V PowerNet.

45 rpm record The standardized phonograph recording speed selected for the single song record. Warren Rex Isom explains the reasons in his article, "Before the Fine Groove and Stereo Record and Other Innovations," published in the Journal of the Audio Engineering Society, October/November, 1977, Vol. 25, No. 10/11, pp. 815-820. One popular belief is that 45 rpm was selected because 78 - 33 = 45. While not too far off, it was a more practical engineering matter that created the ballpark number, and perhaps that mathematical nicety determined the exact number. Once marketing decided on a 7-inch disc with 5 1/2 minutes of playing time, and knowing the groove details and cutter restrictions, the speed satisfying these conditions is 45 rpm. See Record Speeds.

55S Model number for Shure's first single-element unidirectional microphone (called Unidyne), recognized as the first truly practical and affordable directional mic.

60 The base of the Sumerian number system (as opposed to our base-10 number system); the degree is derived from the Babylonian base 60 numerical system. Hours and minutes are similarly divided into 60 (of course, there are minutes of time and minutes of angle - there are 60 minutes in a degree, and, similarly, there are seconds of time and seconds of degree - there are 60 seconds in a minute, 3600 in a degree). [Why 60? Nobody seems to know.]

62 miles Space begins this distance above the earth.

70-volt line See constant-voltage.

74 minutes The maximum length of music on a CD; reason: so all of Beethoven's Ninth would fit on one CD.

77A Model number for RCA's ribbon microphone invented by Dr. Harry F. Olson; followed up by the art deco Model 77-DX.

78 rpm record First standardized phonograph recording speed (exact speed was 78.26 rpm for 60 Hz power and 77.92 rpm for 50 Hz power). The reason for 78 rpm is explained by Warren Rex Isom in his article, "Before the Fine Groove and Stereo Record and Other Innovations," published in the Journal of the Audio Engineering Society, October/November, 1977, Vol. 25, No. 10/11, pp. 815-820. The short summary is that the first machines were hand cranked and a comfortable speed was heartbeat rate — between 60 and 90 per minute. (Interestingly, the same cadence as marching bands and the same speed recommended for hand cranked farm equipment.) When it became time to standardize, Victor machines operated at 78 rpm, while competing Edison machines used 80 rpm, but Victor was the predominate sales leader so it was picked for maximum compatibility. The exact speed of 78.26 rpm came from a simple gearing reason: For a 60 Hz synchronous motor, and a simple worm-gear drive, a ratio of 46 to 1 turned the table at 78.26 rpm and synchronized with the line. See Record Speeds.

94 dB-SPL Equals 1 Pascal = one newton per square meter, which is the standard used to measure microphone sensitivity.

100 MPH The speed at which a sneeze travels out of your mouth. (Snapple Real Fact #58)

160 Refers to the dbx 160 Compressor/Limiter designed by David Blackmer in 1976.

-174 dBm/Hz The power in a one hertz bandwidth of a thermal noise source at the reference temperature of 290 kelvin (approximately room temperature). A noise floor rule-of-thumb.

216 MPH 3/5 Mile in 10 Seconds (Marty Balin, 1967, Jefferson Airplane Surrealistic Pillow)

232 See: RS-232.

333 Half evil.

360 The number of degrees in a circle.

[Ah, but why you ask? Why 360, and not some other number? The answer lies with the Sumerians and their use of a number base of 60 as opposed to our base-10. Here is a quote from Peter Beckmann's book, The History of Pi:

"In 1936, a tablet was excavated some 200 miles from Babylon. Here one should make the interjection that the Sumerians were first to make one of man's greatest inventions, namely, writing; through written communication, knowledge could be passed from one person to others, and from one generation to the next and future ones. They impressed their cuneiform (wedge-shaped) script on soft clay tablets with a stylus, and the tablets were then hardened in the sun. The mentioned tablet, whose translation was partially published only in 1950, is devoted to various geometrical figures, and states that the ratio of the perimeter of a regular hexagon to the circumference of the circumscribed circle equals a number which in modern notation is given by 57/60 + 36/(602) (the Babylonians used the sexagesimal system, i.e., their base was 60 rather than 10)."

The Babylonians knew, of course, that the perimeter of a hexagon is exactly equal to six times the radius of the circumscribed circle, in fact that was evidently the reason why they chose to divide the circle into 360 degrees (and we are still burdened with that figure to this day). The tablet, therefore, gives ... Pi = 25/8 = 3.125.

[When you work in base-60, 6x60 is a natural choice.]

414 Refers to the AKG C-414 introduced in 1971, the first commercial solid-state condenser mic is still in production and still leads the pack.

432 Hz Alternative tuning choice for those working in the sound healing business, as it is considered best for heart-centered, therapeutic sound work. Hit the link to read all about it.

440 Hz (also seen as A440) The musical note A above middle C that is the general tuning standard for musical pitch.

451 The number of degrees Fahrenheit that paper ignites. Made famous by Ray Bradbury's book, Fahrenheit 451.

485 See: RS-485.

500 Series An industry standard for a 3U card frame 19" rack first developed by Datatronix, then API Audio Products, Inc. in the late 1980s. A few years ago, the current company formed The VPR Alliance, which is the controlling organization. [Historical Note: The term, "lunchbox," was coined by Art Kelm who purchased 4-position 500 Series racks from Aphex, in the '80s, for his clients.]

550 Refers to the API 550A Equalizer designed by Saul Walker in 1968.

618A Model number for Western Electric's first practical dynamic microphone.

642 Model number for Electro Voice Cardline shotgun microphone — the first audio product to win an Academy Award in 1963.

670 Refers to the (now mythical) Fairchild 670 Compressor Limiter designed by Rein Narma in 1959, while at Fairchild Recording Equipment Company in Long Island City, NY.

802.3af See: PoE.

802.11 See: Wi-Fi.

808 Refers to the Roland TR-808 drum machine, believed by many to be the one that started it all.

1034 Refers to the original Philips IC part number: TDA1034, which was made by Signetics after their acquisition by Philips, and renamed NE 5534 along with the more often seen dual version, NE 5532. Though not the first audio IC (that credit probably goes to the National Semiconductor LM 381) the TDA 1034/NE 5534 became the first choice for high-quality pro and consumer audio products. With a Slew Rate of 13 V/µs, a bandwidth of 10 MHz and a noise performance of 4 nV/√Hz, it set the standard for all audio ICs to follow.

1073 Refers to the Neve 1073 Console Module designed by Rubert Neve in 1970.

1089 A mathematical magic number: take any 3-digit (all different) number, reverse it and subtract the smaller from the bigger; now reverse that number and add to the previous number and you get 1089—every time; for any 3-digit number where the digits differ; amazing, but true.

123  3-digit number with different digits
321  reverse it
123  subtract
891  reverse
198  add
1089 Voilà!
[Note: if an operation produces a 2-digit number then you must add a leading zero. Each operation must be with three digits.]

1176 Refers to the Universal Audio/UREI 1176 Peak Limiter designed by Bill Putnam in 1968. First use of FETs in audio acting as voltage variable resistors for gain control.

1394 See: IEEE-1394.

1999 Song by Prince recorded in 1982, which became his most popular.

2182 kHz Maritime international voice distress/safety/calling frequency.

4810 The number engraved on the nib of every Montblanc fountain pen, representing the height of the Mont Blanc mountain in meters. Mont Blanc in the French Alps is the highest mountain in Europe and the company's namesake: a symbol for the highest quality standards reached with the products named after it.

5532 Refers to the original Signetics NE 5532, which is the dual version of the NE 5534, which is the renamed part number for the original Philips TDA 1034.

8028 Refers to the most famous Neve 8028 analog mixing console.

500,000 bicycles = 1 megacycle.

1,000,000 aches = 1 megahurtz.

1,000,000,000,000 microphones = 1 megaphone.

AES - Audio Engineering Society