Two-band tone
Video tapes and digital film files contain image and sound firmly linked and conveniently together on a data carrier or in a file. However, this has not always been the case. Because until the replacement of photochemical film production by video tape technology and later recording on digital storage systems, image and sound were recorded on separate devices: the image was recorded with the film camera and the sound on magnetic tape or as optical sound on a separate film strip. Hence the name two-band tone or two-band process. A fundamental problem with all the techniques used was to keep picture and sound in sync through all recording and processing steps until the final playback.
The development of two-band sound in professional film production
When silent film learned to speak at the end of the 1920s (one of the first sound films for cinema screening was the US production “ The Jazz Singer ” from 1927), the problem of the synchronous coupling of film image and sound recording quickly arose. After the first unsuccessful attempts to couple records and film projectors , the optical sound process was developed :
Optical tone method
Here the sound was recorded by means of a so-called sound film camera parallel to the film camera on a perforated film, which exclusively recorded the sound signals in the form of exposed light pulses. Synchronization control systems did not exist back then. In order to avoid that the wow and flutter of the different devices led to a divergence of image and sound after a short time, the camera and sound recording film were perforated identically and both devices were coupled with a mechanical shaft. During post-production, this mechanical coupling was retained on the editing table and in the recording studio. For the demonstration copies, a reduced sound strip was exposed to the side of the film image. Only then were the film image and sound synchronized during the screening. At the same time, this had the advantage that bulk copies could be made in one process.
Disadvantages of the optical tone method
A low signal-to-noise ratio generated high levels of background noise (noise) and the dynamic range (loud / quiet difference) was very low. Large differences in level in a recording situation therefore caused major problems, and the actors were also only allowed to nuanced their speaking volume in order to be clearly audible. In addition, the film material is prone to damage such as scratches, which can appear quickly even with careful handling. This is more noticeable in the tiny sound track than in the picture through interference.
Perfoband process
For filming outside the studio, mechanical interconnections were not very practical anyway. With the advent of magnetic tape technology, the perforated chemical sound recording film has been replaced with a magnetic film ("perfoband"). It was a tape with perforation holes in the same format as the footage. The synchronous coupling was carried out by means of a pilot tone : A generator attached to the film camera generated an alternating current of 2 Hertz per film frame (i.e. 48 Hertz at the usual cinema film speed of 24 frames per second); this pilot tone was transmitted to the sound recorder by cable. There he was amplified and controlled the perforated tape. As a result of the large volume Perfoband rolls, however, the recording devices were very unwieldy.
Tape method
With the advent of small, robust tape recorders with studio quality in terms of synchronization, signal-to-noise ratio and frequency response, such as the Nagra , sound recording finally became mobile. Now you could record on a standard ¼ inch wide tape (called "shoelaces" or "laces" for short). Here, too, the pilot tone was used for synchronization: the pilot tone alternating current was recorded with a further pulse head in the middle of the tape. To prevent the pilot tone from being audible, the recording was made with two simultaneous pilot tones, one of which was 180 degrees out of phase. As the two signals canceled each other out, the pilot tone remained inaudible. Only one phase was used for the subsequent coupling. This also compensated for shrinkage or expansion of the recording tapes as a result of storage.
The pilot tone from the tape later controlled the dubbing system, the sound was posthumously dubbed onto Perfoband and this was further processed synchronously on the editing table and in the sound control room.
When editing films, it was helpful if the film strip and the tape had the same format and had identical perforation holes. The image and sound of the individual scenes could be measured and controlled by the length of the two media.
This procedure was used by broadcasters for current television reporting as standard until the 1970s. The image was recorded on 16 mm reversal material (positive film) and the original was cut. The sound was recorded on site with a portable tape recorder (e.g. Nagra) on commercially available tape ("laces") and copied to Perfoband for further processing in the cutting room and recording studio. This was also broadcast. Instructional and information films were also produced in a two-volume process. However, the screening copies usually received an optical soundtrack.
Quartz control
In the 1980s, the film camera and tape recorder were given a quartz control system , which ensured that the camera and sound recording were synchronized. This saved the need for a cable connection between the two devices, which was a hindrance in practice and was occasionally responsible for failures due to undetected cable breaks.
Two-band sound in the amateur area
Until the advent of tape recorders for home use in the 1950s, amateur film remained silent. In any case, the film cameras for the normal 8 and 16 mm amateur format usually did not have an electric motor, but a spring mechanism to wind it up. Because of the large wow and flutter, a synchronicity of image and sound could not be achieved even approximately. But even with cameras with electric motors, image and sound could only run synchronously with relatively complex and expensive devices. Therefore, these procedures remained the domain of particularly committed film amateurs, who often came together in associations (e.g. BDFA - Federation of German Film Amateurs or Authors). In this environment, important and high-quality documentaries or (less often) fiction films were made, which today can be of historical value. Different approaches and technical procedures developed:
Setting to music afterwards
If complex equipment for synchronous sound was not available, the sound processing took place afterwards. With the tape recorder, background music could be played during the demonstration, of course unsynchronized for the time being. After a short time, picture and sound diverged. With longer films, differences of one minute between picture and sound were quickly reached, depending on the "current conditions" of the projector and tape recorder. Some manufacturers such as Eumig and Bauer began to bring out projectors that could use “feeler wheels” to sense the speed of the running tape and, within certain limits, to orient themselves on the tape. This solution didn't work exactly, but it was sufficient for music and commentary on short films. Lip synchronicity could not be achieved with it. A lack of synchronicity in speech or distinctive sound events is immediately noticed unpleasantly by the human brain.
Live tone cameras
The film sound only became more widespread in the amateur sector with the spread of Super 8 film in the easy-to-use cassette. In 1973, the Kodak company presented a variant in which the film strip was provided with a magnetic strip on the edge, on which the sound could be recorded in the camera, in principle like in a miniaturized tape recorder (see live sound cameras ). However, the sound quality was very limited due to the system. The piste tone only had the frequency spectrum of a better phone. In the amateur field, for example, possibilities were sought to couple external tape devices with the cine film cameras. Because with a good home tape recorder, hi-fi quality was easily possible back then.
Standard sound system ETS
In the 1960s, Günther Grothe from the Federal Association of German Film Authors (BDFA) developed the so-called standard sound system ETS , the development of which resulted in DIN standard 15970, which precisely defines the technical parameters. Originally, two coupling mechanisms were planned: once with the recording of a 1000 Hz pulse per image and once with the recording of a 1000 Hz pulse per 4 images. The controls for the latter process could be operated without electronics, namely exclusively with mechanical relays. This is the reason why this method is preferred in the amateur sector.
Here the impulses from the slave (i.e. from the camera or projector) were counted and compared with the impulses from the master (in this case from the tape). Depending on the difference, the slave system was run faster or slower until the pulse counts were equal again.
With the ETS sound process, the tape controlled the projector, since wow and flutter in the sound can be noticed immediately while they are hardly noticeable in the film image. However, this fact made it almost impossible to subsequently copy the ETS two-band sound onto the sound track of a current projector: there were often wow and flutter and sound howling.
The ETS process quickly became obsolete with the emergence of sound film projectors from the Bauer company, because they always offered complete synchronicity thanks to magnetic sound edge tracks glued to the film, and even a second sound track with Super-8 due to the so-called compensation track. This made it possible to produce usable sound mixes, even though the sound of the pistes was not particularly good due to the system, as mentioned above.
In the 1970s, the impulse reduction and other problems of the ETS process created a gap in the market for many synchronous system manufacturers who relied on 1: 1 controls.
Synchronous systems
The market for synchronous systems boomed quickly. In the 1970s, the serious (and financially wealthy) film amateur was able to choose from around 20 different sync systems: Casy, Gigge, Synputer, HVS, Bröker and many more. Ultimately, only the Gebuhr company (replica of the Gigge synchronous film devices), an innovative computer system with extensive in-house programming, was far ahead of its time. The Multisyn fee, which is still available, can still be combined with almost all amateur and professional synchronizing systems.
Perfoband
A disadvantage of the pulse-controlled systems, however, was that the pulses could not be seen on the tape; they were mostly shown digitally on a display of the control unit. This often made post-editing of the film a bit tedious, because sync pulses and film perforation holes had to be counted.
That is why there have been various attempts at synchronous coupling with perforated tape in the amateur sector, similar to the above-mentioned professional league with the Perfoband. Super 8 magnetic film (“cord tape”) had the same dimensions as the film strip, but brought no improvements, because the Super 8 film delivers a tape speed of around ten centimeters per second at 24 frames per second - a lot at the time too little for usable sound improvement.
One system, however, was able to hold its own very well on the market: The so-called "oblong hole perfoband" was developed by Gigge Synchronfilm GmbH: Holes were punched in the middle of a standard high-quality tape. With a converted Uher-Report tape recorder or an externally attachable forward and backward counting Perfo reading head, these were counted and compared with the impulses of the projector. Various inexpensive handicraft instructions for self-construction for the control were available free of charge in amateur film magazines such as the "Film and Sound Magazine", which was very popular at the time. They ensured that the system was well distributed. However, the formats of perforated tape and narrow film perforation were also different here. Counting while editing the film was necessary again!
The manufacturers of professional film cutting tables such as Steenbeck and Schmidt offered the coupling of a Super 8 with a 16 mm magnetic film (Perfoband). However, the different dimensions of image and sound strips when editing the film were again rather impractical.
Generally speaking, all of the synchronous systems of that time were unsuitable for staging with actors. Setting a dialogue scene with counter cuts by two interlocutors to music is doable, but tedious. Maintaining synchronicity requires more effort than assembling the content of the film pieces. However, only a minority of film enthusiasts who were enthusiastic about synchronous sound were concerned with staged films. The majority filmed documentary in every form. The sound consisted of a live atmosphere and interviews, and for these purposes the synchronizing systems offered sufficient scope for creativity.
Digitization of narrow films with two-tape sound
There are various options for copying cine films to modern digital formats. It starts with the simple "filming" of the screen with the camcorder in real time, which works surprisingly well for "home use". Important film material can be professionally copied "frame by frame" - possibly even with "flying spot scanning" in which a laser point successively scans the film images. The adaptation to the original projection speed of the film takes place via computer editing software with which the sound of the film is also copied without any synchronization and then adapted to the film image-precisely. The multi-track technology of the computer editing software also enables simple new or additional dubbing.