The Recording Process:
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In the age of digital audio and video, most people born from the 1980s on have been subject primarily to cleanly recorded music either nearly or completely devoid of hiss or other noises. Even for those born as early as 1960, they enjoyed relatively high-fidelity music for 20 years and stereophonic or quadraphonic (an early incarnation of surround sound) reproduction, and simply got used to the seemingly subdued level of noise. But for the 70 years leading up to that time, recording engineers and designers were constantly in search of ways to produce music at higher fidelity (literally faithfulness to the original) with minimal noise. This section is just a brief overview of that search, along with minor technical information, some observations, and commentary about the results of these engineers. For a more detailed history, the author highly recommends the latest revision (1994) of From Tinfoil to Stereo, an interesting look at technical developments and legal struggles to create better recordings.
When Thomas Edison first recited, "Mary had a little lamb...,"
Thomas Edison with one of his early Dictaphone cylinder machines. |
into the horn of his cylinder recorder onto a piece of tinfoil, he was using his invention for the purpose it was developed for - as a dictating device. Even though the human voice can cover a wide range of the widely accepted 20-20,000 Hz (alternately cps or cycles per second) frequency spectrum, from low bass notes to the crispest sibilants, the average male or female speaking voice can be captured tolerably well within a very limited portion of that spectrum. So the only fidelity that was necessary was functional. The small horn that Edison used for both recording a playback provided little more than that, covering a range of maybe 400-1,500 Hz. Even that range varied, depending on the speed at which the cylinder was cranked. Edison really did not consider at first the potential viability of his invention as a form of musical archive, and had soon turned his attention to making better light bulbs. But once somebody inevitably did try to record music on this device, it was obvious that something had to change to accommodate the required wider frequency spectrum for palatable reproduction, at least in the range of about 150-4,000 Hz. Thus was born the recording engineer.
The first technical issue, aside from improving on the materials used for the cylinder which is secondary to reproduction on earlier machines, was how to put larger AND smaller sound waves onto a disc. There were compromises where the recording equipment had to be redesigned to accommodate the instruments, and instrumentation had to be altered to accommodate the recording equipment. Increasing the size of the wooden or stiff fabric recording horn was an easy solution, and horns typically grew to a size of three to six feet in diameter. Since sound waves for the upper octaves are relatively short, but those in the lower parts of the spectrum tend to be longer than three feet, the size of the horn made a difference as to how effectively low frequencies could be captured. If the wave was longer than the diameter of the horn, some level of wave alteration occurred so that only partials of notes from bassoons or tubas were captured, as opposed to their fundamental frequencies, giving them a thin or hollow sound. As for the reception of high frequencies, the recording diaphragm connected to the engraving stylus had to transmit those as well as all the low frequency information, so the grade and thickness of the metal or glass used for the diaphragm often dictated the quality of these frequencies. This was sometimes a difficult prospect if the horn was poorly designed to favor only the lower frequencies.
The shape of the horn also made a difference. As with brass instruments, such as the flugelhorn and trumpet which are similar in size but different in tone, the differences in the bore of the cone can favor certain frequencies while canceling out others. This creates spikes at certain frequency levels, something that can clearly be ascertained on the earliest acoustic recordings up through the early 1910s. Also the shape of the bell at the end of cone, as well as the conical characteristics of the bend at the back of it could effect what sounds were captured and which frequencies rolled off. The total length of the recording horn as well as the placement of the instruments also determined variances in volume between recordings. For example, many Columbia recordings are noticeably more subdued than Victor titles with similar instrumentation, indicating different recording practices between the two companies. In early cylinder recordings, which required instrumentalists or vocalists to perform multiple takes in front of an array of acoustic recording horns, marked differences in volume and instrumental balance can be noted between individual cylinders, based on the location of the recording horn in relation to another cylinder's horn. The advent of mass production ushered in by the disc recording processes helped to negate these differences.
Due to the limited frequency responses of many horn designs, engineers had difficulty in effectively recording certain instruments or voice timbres. They would use varying sizes of horns depending on the source, and could network up to four horns in some cases into one recording lathe sound box, effectively an early form of mixing. One of the most obvious instruments that appears only infrequently in the earliest records as a solo instrument is the piano. Most pianos tended to sound rather tubby, favoring the tenor frequencies above all others. Thus there is little recorded piano ragtime or accompanied popular song prior to the mid 1910s when many of the spectral problems were countered with new horn shapes. Since sound velocity was the key to creating recordings that would play back at appreciable volumes, many of the early recordings feature brass-based ensembles, since stringed instruments did not transmit nearly as well. Amplifying horns were sometimes attached to violins to even the playing field. In an effort to keep all instrumentalists as close to the recording horns as possible, they were often crowded together on risers with the soloists and softer instruments towards the front. This arrangement often meant the audible omission of drums and bass instruments, even though they were at the sessions, but it was necessary due to the limited reception range of the recording horns.
One variable that needs to be factored in is that of speed.
A Victrola turntable with a speed control located at the lower left corner of the picture, with a practical range of 74 to 82 rpm. |
The earliest cylinders were turned at about 60 rpm (revolutions per minute) and varying recording speeds of 90 to 120+ were used during the 1880s and 1890s until a consistent industry standard of 160 rpm was settled on around 1901. The increase in speed allowed for more accurate cutting of grooves in the cylinder yielding higher fidelity, but shorter playing times. The initial capacity of cylinders was around 120 seconds when cut at 100 grooves per inch, but later technology made a 4 minute cylinder a possibility at 200 grooves per inch, the industry standard until the eventual demise of the format. The change in format also required owners of existing cylinder players to buy conversion gears to properly track the newer cylinders. Discs went through similar growing pains in regards to speed. Some were recorded as low as the mid 50s and up into the 90s, making matching of the correct speed difficult without a pitch reference and knowledge of what key a recording was done in. The eventual industry standard, officially adopted in 1924 but often used from the mid 1910s on, became 78 rpm. This yielded a typical 3.25 minute limit for 10" discs, one that was extended to 3.5 minutes once electronic recording was applied. 12" discs were capable of 4.75 minutes of material on average. Even after the standard was set, some engineers deliberately undercranked recordings to get longer performances on a side, requiring adjustments in speed at the consumer's end, or more often an altered performance at 78 rpm playback.
As previously mentioned, the grooves in discs were cut laterally or from side to side. This meant the louder and lower the frequency, the wider the groove that was needed to properly reproduce it. This has remained true for records throughout the 20th century. But until the engineering was available to control the inward rate of the recording stylus towards the middle of the record, a standard velocity was set which created the time limit, which in part contributed to the length of popular music selections up through the early 1950s. But the standard rate for acoustic recording also allowed for a lot of headroom in the recording, and therefore very little distortion from overload, something that was inherent with the advent of electronically recorded discs.
The exception to the disc format was Edison's Diamond Disc system. The grooves were cut vertically, or using a hill and dale technique. Since the bulk of stylus travel was absorbed into the depth of these rather thick (1/4" on average) records, the potential for recording time increased to over 5 minutes. However, Diamond Discs were incompatible with systems that played laterally cut discs, and the reverse was true. The playback stylus for each system was designed only to travel in the direction of the recorded groove, allowing virtually no latitude for grooves cut 90° from what was expected. So while the sound from many diamond discs was in many ways superior to cylinders and standard discs (albeit with increased surface noise), the incompatibility with the format favored by a majority of players helped lead to its demise. |
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