.

Pickup and recording work requires a mixing console containing microphone amplifiers, tone control circuits, and mixing circuits, etc. Incidentally, with regard to mixing consoles in general, many mixing console manufacturers appeared after WWII in the UK, where demand for loudspeakers for the many giant halls that exist there was particularly great, and they have retained a large share of the market even to this day.

If real-time processing can be carried out digitally using high-speed multipliers with control programs and amplifiers, tone control circuits, mixing circuits from analog mixers, then digital mixers can be realized.

The development of digital mixing consoles began at various companies during the mid-1970s. At the time, semiconductor technology was making similar progress to that of digital media like the CD, reaching a practical level by the early 1980s; but issues such as the delay of convenient and cheap high-speed multipliers in reaching the market, the need for research to solve sound quality degradation caused by the occurrence of conversion errors and arithmetic errors, and delays in developing a machine interface for the mixing console itself held them back until the mid-1980s, after CDs were introduced.

Editing involves finishing a work and correcting any mistakes made during the performance. Important conditions for editing :
.

• (1) The ability to search for the place to be edited while listening to the piece or looking at the waveform.
• (2) The ability to join two edits together.
• (3) No discontinuities (click sound) at splices.

.

Prior to World War II, editing was restricted to setting up several disk record players and disk recorders, synchronizing them, and sending the output to a recorder.

In the 1950s, when magnetic recorders that used magnetic tape were introduced, tape splicing became widespread. When cutting and splicing, the technician slowly moves tape by hand, listening to the sound to find the edit point, which is then marked. Then the marked tape is cut diagonally to avoid a clicking sound, and splicing tape is used to reconnect it.

Although narrow recording tape with a small number of tracks was cut and spliced, multitrack recordings on wide tape were not. Such tapes were corrected by re-recording over the parts of the tracks that contained mistakes.

These multitrack recordings are combined into a small number of tracks in a process called mixing down or tracking down to make the stereo sound fields, etc., of the completed recording.

In the early days of digital recording, recordings from fixed head recorders with a small number of tracks or from four-head VTRs were edited by (mechanicly) cutting and splicing, and recordings from helical scanning VTRs, such as the U-matic, were edited by copying.

Although this kind of editing was done by splicing or copying, a random access editor that used a mainframe (IBM plug-compatible machine) hard disk unit (controlled by a TI 9900 microprocessor) for use in content editing environments was introduced in 1981, just before the introduction of the CD.

This enormous editor is shown in Fig. 5.36.

This editor increased editing efficiency significantly, and contributed toward improving the quality of sound sources for CDs and increasing the efficiency of production.

Today, random access editing can be done at home with simple software, thanks to the existence of cheap personal computers with plenty of storage capacity.

With classical music, where the same music is recorded several times with different musicians, there is a limit to the ability of people to achieve recording better that the one before them, so more edits are necessary.

In some cases, an LP or CD with approximately 50 minutes of playing time will require editing in over 200 or even 300 locations. In such cases, the question of how to guarantee the artistic qualities of the performance is important.

Later, the Denon DN-050MD digital mastering/mixing console for cutting (Fig. 5.37) was released, establishing a digital process from recording through to the cutting amplifier.

Before magnetic recorders were introduced, master disks (wax disks made of montan wax with beeswax and vegetable wax) were cut in disk recorders and then sent to be duplicated.

After magnetic recorders were introduced, audio was put through editing, mixing down, further adjustment and inspection processes, and then the (final) content for the destination disk record was put on a magnetic tape (called a master tape) and sent to the cutting room. The cutting process was called “cutting” or “disk mastering.”

During cutting, the cutting stylus of a cutting machine (a cutting lathe with a groove cutting unit called a cutter head attached) cuts a master disk called a lacquer.

This lacquer disk consists of a flat aluminum core disk coated with a mixed solution of nitrocellulose, benzole, butyl acetate, butyl alcohol, ethyl acetate, DOP, castor oil, ethyl alcohol, and dye.

The cutter head was usually a single-resonance system with a resonance frequency of around 1 kHz, and with the addition of a lot of dynamic feedback (30dB or more), a flat characteristic from 50 Hz to 18 kHz could be obtained relatively easily.

To allow dynamic feedback, the cutter heads were equipped with sensing coils as well as driving coils. These sensing coils could not check the grooves themselves, but obtained signals from the movement of the cutting stylus, allowing sound quality to be checked during cutting. Therefore, the technician would usually listed to this signal during cutting to check the state of the cutting system’s operation.

The disk records are essentially limited by their speed limit as determined by their rate of rotation and groove diameter.

With regard to the driver of the cutter head, it is necessary to drive an amplifier with enough output (300 Watt or greater, with an 8 ohm conversion in the case of the Neumann SX-74, which was a typical cutter head) for the speed limit of the record with the intended rpm and groove diameter.

Another limitation of cutting systems is that the level is the amplitude of bass signal levels at the cutter head (± 150 microns in the case of the SX-74).

However, as the maximum amplitude of a normal disk record is approximately ±50 microns, an amplitude limitation of ±150 microns is more than sufficient. When records are cut with a signal close to the maximum amplitude of the cutter, playing time is shortened and tracing is difficult, making stable reproduction a challenge.

The preceding paragraph discussed the limitations of the cutting side; there are limitations that appear during playback also. One limitation of reproduction is the playback stylus’ radius or curvature (die Krümmung) (e.g. a 16.5-micron spherical stylus). Another is the diameter of the groove, and then there is also the noise created on the disk during playback.

Figure 5.38 illustrates the limitations (excluding noise) when recording and reproducing (LP) disk records.

The playback limitations are more noticeable toward the interior, and although this can be improved by reducing the radius of curvature (die Rundung) of the playback stylus, caution is required as this can sometimes damage the grooves on the disk.

Although Fig. 5.38 does not show noise from the disks as a lower limit, it is still important to take noise into consideration, and it is necessary to reduce it as much as possible by taking other measures, such as improving the materials from which disks are made.

Figure 5.39 shows the shape of a cutting stylus.

To improve the machinability of the grooves during cutting, and to reduce noise (by improving the sharpness of the grooves, nichrome wire was wound around the tip of the cutting stylus as shown in Fig. 5.39 and heat was applied.

In addition, inert gas (helium) injection is widely used to prevent the coils that drive the cutting stylus from breaking due to oxidation and heat.

Various kinds of playback stylus tip shapes and their relation to contact area are shown in Fig. 5.40.

When cutting lengthy stereo content on a disk record, in order to cut the left signal at 45 degrees and the right signal at minus 45 degrees (or cut the sum of the left and the right horizontally, and the difference vertically), it is necessary to know the groove pitch and depth in advance, and set the pitch and depth that is most appropriate for the content.
.

Magnetic recorders/reproducers (see Fig. 5.14 for an example) and digital recorders/reproducers (see Fig. 5.23 and 5.29) used in cutting (mastering) are equipped with an "advanced head" (Vorschau-Kopf) that enables them to know what kind of signal will come before the cutting signal arrives, sets the pitch (the distance between grooves) of the cutting lathe, and also sets the average depth of the groove by regulating the vertical controller part of the cutter head.

If the average pitch is too narrow, then the groove will come into contact with the adjacent groove (angrenzenden Rille), causing sound from the adjacent groove to be heard; and if it is too wide, then extended recording becomes impossible.

Moreover, if the average depth is too shallow, then the groove will be broken and the playback stylus sill not be able to track the groove properly during playback; and if it is too deep, then extended recording becomes impossible, and in extreme cases the groove will reach the aluminum core of the lacquer disk, damaging the cutting stylus.

Extended recording also becomes difficult if there is a large difference in bass between the left and the right signals, so elliptical equalizers (which control the difference in bass between the left and the right), etc., are used.

Using these equalizers has the merit of allowing records to be played back with old monaural cartridges, to a certain extent.

Although cutter heads are an inconspicuous technology as compared with cartridges, rarely being noticed, they are one of the fundamental technologies that support analog disk records, and, as described in 4.3, their foundation was laid during disk recorder development prior to WWII.

Some typical cutter heads and cutting machines will be presented in the following paragraphs.

The four cutter heads shown in Fig. 5.41 to 5.44 are typical cutter heads from the end of the SP (78er) era, through to the early stages of the LP and the stereo era (1959).

Blumlein’s cutter head used permanent magnets and electromagnets, and was enormous in size, as can be seen by comparing it with the Neumann SX-74 (Fig. 5.41), which was the most widely used cutter head when stereo was thriving (aufblühen).

Figure 5.48 shows a Scully (USA) cutting lathe (eine ganze Schneidmaschine) and its components as an example of a cutting lathe (cutting machine) equipped with the cutter head shown above.

A number of different cutter heads made by various companies during the golden age of stereo LPs are shown in Fig. 5.45 to 5.47.

Figure 5.49 shows a wax disk-era cutting lathe made by Denon.
Figure 5.50 shows a cutting lathe from around 1956 made by Denon.
Figure 5.52 shows a Scully (USA) cutting lathe with a Westrex 3D cutter head. (Nippon Columbia Co., Ltd.)
Figure 5.51 shows a Lyrec cutting lathe with an Ortofon cutter head (both Danish).
Figure 5.53 shows a Neumann (Germany) cutting lathe with a Neumann SX-74 cutter head.

When direct-drive turntables for consumer record players began to be introduced, direct-drive turntables for cutting machines also appeared. A Denon direct-drive motor is shown in Fig. 5.54. Figure 5.55 shows an example of a cutting machine used in the present day.

Behind the cutting machine is a tank (eine Gasflasche) containing helium for cooling the coils in the cutter head.

The helium tube passes through a flow meter on the right-hand edge, through an opening in the front of the SX74 cutter head, and injects helium over the coils.

Lacquer disks placed on the turntable are held onto it by means of suction from the pipe in the center and holes in the top of the turntable. The pickup beyond the turntable is used for correction and checking the sound quality, etc., and the Denon DL-103 cartridge (shown in Fig. 4.12 and 4.13) is still used to this day. The microscope to the left of the turntable is used to check groove geometry and cutting state.

As described above, there exists an upper limit to the speed of disk records (Anmerkung : wir sprechen von der "Schnelle") that is determined by their rate of rotation and groove diameter, and an upper limit to the amplitude of the signal that depends on the ability of the cutter head and the playback head to trace it.

There are also limitations on playback that are determined by the radius of curvature (Krümmung) of the playback stylus and the diameter of the groove on the record.

In addition to these upper limits, there are also lower limits, such as the noise on the disk itself. In many places there were attempts to introduce equalization curves that were optimally suited to music reproduction that took these limitations and also the frequency distribution of the content into consideration.

The frequency distribution level of signals was therefore measured for types of content, such as such orchestral music, etc., that it was thought would require an exceedingly large dynamic range.

Unfortunately, this hard work did not bear fruit during the era of electrically-recorded SP records, and these equalization curves were not able to be standardized.

As the various companies adopted different equalization curves after the introduction of LP records, records players were equipped with at least 11 different equalization curves, which had to be selected with a switch according to the record (the various labels).

This problem was solved when an equalization curve was standardized in the form of the RIAA curve in February 1954 by the "Recording Industry Association of America®" (RIAA).

The same curve was also adopted by the IEC, and it was later revised in 1976. The RIAA and IEC equalization characteristics are shown in Tables 5.5 and 5.6 respectively.

Die Zahlen sind viel zu unübersichtlich und haben für einen Laien viel zu wenig aussagewert.
.

The IEC standard shown in Table 5.6 includes the equalization curves for 78er SP records (the “Coarse Groove” columns).

The LP columns (Fine Groove) (Anmerkung für Mono und Stereo) in Tables 5.5 and 5.6 differ because the frequencies set by the RIAA and the IEC are different. It is widely known that humans perceive the difference in pitch between 100 Hz and 200 Hz to be the equivalent of the difference between 1 kHz and 2 kHz and not 1 kHz and 1.1 kHz.

As this corresponds with frequencies expressed logarithmically, even though the frequencies specified as standard frequencies are chosen differently in the bass range, they are mostly chosen evenly from the logarithmic axis.

As the characteristic can deviate on the recording system or the playback system at higher frequencies, both the RIAA and IEC specify higher frequencies more closely.

These equalization curves are designed to effectively utilize the dynamic range of disk records that exists between the upper limits imposed by speed and amplitude and the lower limits imposed by noise levels (caused by the disk materials).

To decide on these levels, it is necessary to consider the sound pressure levels and the frequency distribution of the sound source in question.

Note that these equalization curves were established with the sound pressure and frequency distribution of a front-row seat at a full orchestra performance in a concert hall (where especially high sound pressure levels are needed) in mind.

The results of Bell Laboratories’ pre-WWII research (completed with the cooperation of the famous conductor Leopold Stokowski and the Philadelphia Orchestra) live on in the form of these equalization characteristics.

When changing the recording media from records to cassette tapes and CDs, different equalization characteristics are required. Cassette tapes actually need a different equalization curve, and CDs have a simple equalization curve called “pre-emphasis” for people who want to use it; this is set on or off on the CD itself, and a de-emphasis circuit automatically removes the emphasis when the CD is played back.

As described above, equalizers for analog records were standardized for the frequency distribution of orchestral music, but analog record cutting engineers are vexed (zerstritten) by music and sound effects that have a completely different frequency distribution from western orchestral music.

One such type of sound is the sound made by insects, for example, the chirping of katydids. In Japanese traditional music is one type of music in which there are instruments that produce sounds that contain such high-frequency components.

The frequency distribution of such music is skewed to the treble region, and includes variations in amplitude (amplitude modulation) and slight variations in frequency (frequency modulation) in the treble range.

If nonlinearity (which is the primary cause of distortion at higher frequencies) exists, then the small amplitude and frequency variations in the bass that were inaudible in the original sound become audible, and if this is emphasized by the equalization curve (which raises the bass), then the resulting sound will not remotely resemble the chirping of a katydid.

Such phenomena occur when the band is widened unnecessarily and the signal is transmitted with uncontrolled bands (nonlinear bands), therefore it is important in all cases to restrict the signal to manageable transmission bands.

The systems of recording and reproduction can generally be divided into entities such as record companies (which record sound) and households (which reproduce it), with both parties having the same point of contact: disk records.

Special records, called frequency sweep records or test records, are used to manage the characteristic of the playback system at this point of contact.

To make frequency sweep records, it is first critical to establish methods of measuring the grooves, and then it is necessary to accurately measure groove displacement/shape, wavelength and cutting direction, etc., using methods such as those shown in Table 5.7.

.

• i) Light pattern method
• ii) Light pattern method using interference (B-line technique)
• iii) Variable speed method
• iV) Methods using interference microscopes
• V) Methods using electron microscopes

.

Optical microscopes are installed on cutting machines for inspecting the sides and the bottoms of the grooves for damage, and for checking the approximate size and spacing of the grooves. These microscopes are used whenever a disk is cut.

The Buchmann-Meyer light pattern method that was invented in 1930 was the most widely used method used for measuring the amplitude and velocity of the groove during cutting without physical contact.

This method takes advantage of the fact that the width of the reflection of a beam of light projected onto the face of the groove directly corresponds with the velocity amplitude of the signal being recorded.

With the light pattern method, the recording wavelength shortens as the signal frequency increases, causing the reflected light to scatter, and making measurement of a well-defined band of reflected light more difficult.

The light pattern method offsets this weakness with a fringe (ausgefranste Ränder) pattern, an improvement introduced by Buer in 1955. On the other hand, if the signal frequency decreases, then it becomes difficult to cut a fixed velocity amplitude due to the amplitude limitations of the cutter head, so measurement accuracy using the light pattern method decreases as velocity amplitude decreases.

The variable speed method, which varies the playback speed and calibrates the levels of different frequencies, is an effective means of ensuring accuracy under such conditions.

Although absolute calibration is impossible with this method, it is possible to easily carry out calibration and ensure good precision to the extent that pickup remains linear.

Methods using interference microscopes work by observing the grooves under a direct interference microscope and determining the groove displacement, shape, and amplitude from the shape and spacing of the interference pattern.

These methods generally used a light source with a wavelength of 0.546 microns, and the spacing in the interference pattern corresponds to half of this, or 0.273 microns.

When observing a "JIS" reference level 1 kHz sine wave, the theoretical displacement of the groove face (peak-to-peak) is 11.26 microns, allowing approximately 0.1dB of accuracy (supposing a margin of error of 50%).

Crosstalk could be measured to within approximately -38dB, and accuracy can be improved by raising recording levels.

Measurement techniques that use electron microscopy have become an indispensable method of observing the vertical and horizontal cutting angles, the characteristics of the stylus, and the finish from the electroplating stage.

When frequency records are actually made, a number of methods are used in combination instead of relying on a single method.

Table 5.8 shows the main things frequency records are used to measure in playback systems.

.

• (a) Sensibility (reference level)
• (b) Frequency characteristic (ultra-low, audible, ultra-high)
• (c) Playback loss
• (d) Crosstalk
• (e) Distortion (harmonic distortion, intermodulation distortion, etc.)
• (f) Wow/flutter
• (g) S/N ratio (blank groove)
• (h) Electrical impedance
• (i) Mechanical impedance
• (j) Vertical tracking angle
• (k) Phase characteristic (between 2 channels)
• (l) Delay characteristics
• (m) Transient characteristics

.

.
Table 5.9 lists examples of well-known pre-1975 frequency sweep records that were capable of measuring most of the items listed in the table above.
.

.
In Japan, the reference levels on disk records are specified by "JIS" and are therefore not named in a confusing manner, but in other countries, the reference levels and nomenclature are different. Some examples are given in Table 5.10.

It goes without saying that when using frequency records with non-JIS reference levels that the levels must be converted at the time of measurement.
.