The dbx Model 700 Digital Audio Processor was a professional audio ADC/DAC combination unit, which digitized a stereo analog audio input into a bitstream, which was then encoded and encapsulated in an analog composite video signal, for recording to tape using a VCR. Unlike other similar pieces of equipment like the Sony PCM-F1, the Model 700 used a technique called Companded Predictive Delta Modulation, rather than the now-common pulse-code modulation. At the time of its introduction in the mid-1980s the device was the first commercial product to use this method, although it had been proposed years earlier.^[1] An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic circuit that converts continuous signals to discrete digital numbers. ... In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). ... Symbol for stereo Stereophonic sound, commonly called stereo, is the reproduction of sound, using two independent audio channels, through a pair of widely separated speaker systems, in such a way as to create a pleasant and natural impression of sound heard from various directions as in natural hearing. ... An analog or analogue signal is any variable signal continuous in both time and amplitude. ... Composite video is the format of an analog television (picture only) signal before it is combined with a sound signal and modulated onto an RF carrier. ... High-quality PCM audio requires a significantly larger bandwidth than a regular FM audio signal. ... The Delta-Sigma (ΔΣ) modulation is a kind of analog-to-digital signal conversion derived from the delta modulation. ... Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code. ... MacGyver is one of the symbols of the 1980s in America The 1980s decade refers to the years from 1980 to 1989, inclusive. ...

History

Unlike the many digital recording formats that would follow (e.g. DAT and ADAT), the Model 700 had no capability for storage on its own, and relied on an analog recording medium supplied by the user. In general, any high-quality VHS VCR without automatic tracking would do, although 3/4" U-matic or Beta decks could also have been used. If viewed on a monitor, the output stream of a Model 700 looked like analog TV "static" or noise, with slight black bars running down either side. ... This is an article about the digital recording format. ... Top view VHS cassette with U.S. 25c coin for scale Bottom view of VHS cassette with magnetic tape exposed The Video Home System, first released in September 1976, better known by its abbreviation VHS, is a recording and playing standard for video cassette recorderss (VCRs), developed by JVC (with... The video cassette recorder (or VCR, less popularly video tape recorder) is a type of video tape recorder that uses removable cassettes containing magnetic tape to record audio and video from a television broadcast so it can be played back later. ... Sony U-matic VTR BVU-800 A U-matic tape U-matic is the name of a videocassette format developed by Sony in 1969. ... Sonys Betamax is the 12. ...

Early on, the machine was hailed as "the best recording device you can buy,"^[2] and Stereophile Magazine reviewed it positively.^[3] Many people liked the format because it offered more dynamic range than analog tape, but without the "hard clipping" inherent in PCM audio recorders of the time. The Model 700 had been designed from the beginning to have many 'tape-like' characteristics, including "soft saturation," and at a time when most professional and amateur recordists were used to analog tape, this was considered a significant feature. It also offered 14dB more dynamic range than 44.1kHz/16b audio, and because of its very high sample rate (644kHz), it did not contain the same anti-aliasing filters necessary in PCM recorders at the time, which were thought to cause undesirable harmonic interference. Stereophile is a monthly magazine that focuses on audio equipment, such as loudspeakers and amplifiers, and audio-related news, such as online audio streaming. ... An anti-aliasing filter is commonly used in conjuction with digital signal processing and is a filter to restrict the bandwidth to approximately satisfy the Shannon-Nyquist sampling theorem. ...

The device sold for $4,600 in 1986,^[2] and that was without a video recorder on which to store the output, putting it out of the reach of all but the most wealthy home users. However, its target market was professional and studio users, and here it enjoyed relative popularity for a short amount of time as a mastering or mixdown recorder, recording the final output from a multitrack system. Multitrack recording (multitracking or just tracking for short) is a method of sound recording that allows for the separate recording of multiple sound sources to create a cohesive whole. ...

The Model 700 was available in several different versions. In its most basic incarnation, it had two line-level, balanced inputs. One popular upgrade was the addition of one or two microphone preamps, which were installed on removable cards into slots in the machine. These allowed stereo recording directly into the Model 700, bypassing a mixing console. Since the recorder had a significantly lower noise floor than most mixers of the same era, this method made the best use of the system's available dynamic range. Another, much more rare accessory was the Model 700D Disc Mastering Delay. This was a device used for mastering vinyl records, and which attached to a proprietary 25-pin digital output on the back of the Model 700 recorder. Because of the nature of vinyl records (which rotate at a constant angular velocity but at a changing linear velocity with respect to the needle as it moves inwards), it is necessary to speed up or slow down the audio which is being fed to a record cutter in order to preserve the correct pitch. Since the Model 700 did not have the capability of playing back at anything other than 100% normal speed natively (as analog audio tapes do), the Disc Mastering Delay was sold as a solution which enabled this. Line level is the strength of an audio signal used to transmit analog sound information between audio components such as CD and DVD players, TVs, amplifiers, and mixing consoles. ... Balanced audio connections are extremely important in sound recording and production because they allow for the use of very long cables with reduced introduction of outside noise. ... A microphone, sometimes called a mic (pronounced mike), is a transducer that converts sound into an electrical signal. ... A preamplifier (preamp) is an amplifier which precedes another amplifier to prepare an electrical signal for further amplification or processing. ... BBC Local Radio Mark III radio mixing desk In professional audio, a mixing console, mixing desk (Brit. ... In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system. ... Dynamic range is a term used frequently in numerous fields to describe the ratio between the smallest and largest possible values of a changeable quantity. ... 33â…“ LP vinyl record album from the 1960s A gramophone record (also phonograph record, or simply record) is an analogue sound recording medium consisting of a flat disc with an inscribed modulated spiral groove. ... Angular velocity describes the speed of rotation. ...

The Model 700 was developed and sold by the dbx corporation of Newton, Massachusetts, better known for their system of noise reduction for analog tape. dbx, Inc. ... The newton (symbol: N) is the SI unit of force. ... Official language(s) English Capital Largest city Boston Boston Area  - Total   - Width   - Length    - % water  - Latitude  - Longitude Ranked 44th 10,555 sq mi  27,360 km² 183 miles  295 km 113 miles  182 km 13. ...

Technical Specifications

• Dynamic Range: 110dB typical with A-weighted noise 20Hz-20kHz; >105dB unweighted
• Frequency Response: 20Hz-20kHz, sine or pink noise, 100mV, reference record position
• THD: less than 0.05%, 1V input, 1kHz
• Wow and flutter: less than 0.01% unweighted; 0.006% wrms
• Anti-aliasing filters: -3dB at 37kHz
• Sampling Rate: 644kHz
• Bit Rate: 644 kbit/s
• Mic Pre: adds less than 1dB noise, 100 to 1k-ohm impedance
• Max In/Out Levels: +24dBm ^[4]

Theory of Operation

The Model 700 converted analog audio into digital data using a type of delta-sigma modulation, called "Companded Predictive Delta Modulation," or "CPDM" (both trademarked). In a traditional, single-integrated delta-sigma ADC, the voltage of an input signal is compared to the output of an integrator. If the input signal is higher than the integrator's output, a 1 is recorded, and the integrator is given a command to increase by a certain amount. On each clock cycle, the comparison is repeated (and another 1 is recorded) until the integrator's output exceeds the input voltage, at which point a 0 is recorded and the integrator is told to decrease. In this way, the integrator attempts to follow the input signal as closely as it can. When fed a constant-voltage signal (or when the input is removed completely), the output will "idle" and produce a stream of alternating 1s and 0s. A decoder listening to this stream would produce a small sinusoidal or triangle-wave output, even though the correct output should be flat: this is a form of quantization error. The Delta-Sigma (ΔΣ) modulation is a kind of analog-to-digital signal conversion derived from the delta modulation. ... An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic circuit that converts continuous signals to discrete digital numbers. ... An integrator is a device to perform the mathematical operation known as integration. ... Quantization of x using Q(x) = floor(Lx)/L. In digital signal processing, quantization is the process of approximating a continuous signal by a set of discrete symbols or integer values; that is, converting an analog signal to a digital one via analog-to-digital conversion. ...

Where the Model 700 differs from classical delta-sigma modulation is in its replacement of the single integrator with a complex system of comparators and high-order linear prediction filters.^[5] This was done in order to reduce the quantization error, and is accomplished in part by changing the effective "step size" of the encoder based on previously recorded information. (Thereby increasing or decreasing the slew rate.) The system also has two analog pre-processing steps which compress the input signal in both the amplitude and frequency domain, in order to more closely match the abilities of the encoder. This compression is done adaptively based on previously encoded signal, and is reversed on the decoding end.^[6] In electronics, the slew rate is a nonlinear effect in operational amplifiers. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ... Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency. ...

References

Further Reading

• http://www.allaudios.org/detail-7102664.html Archive of a discussion of the dbx 700 by several apparently knowledgeable individuals.
• http://lists.bostonradio.org/pipermail/boston-radio-interest/2004-September/003920.html WGBH-FM Boston used the dbx 700 as its studio to transmitter link.
• P. Nielsen, On the Stability of Double-Integration Delta Modulators, IEEE Transactions on Communications Technology, Vol. COM-19, 1971.
• C. Thoeny, Stability Considerations on Filters Realized with Delta Modulation, IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. ASSP-28 No. 6, December 1980.