Track 2 - Frequency sweep; 5Hz to 22kHz. The pure tone, as illustrated in Track 1, actually sounds rather dull and characterless. But we can still vary such a sound in two important ways. Firstly we can vary the number of cycles of oscillation which take place per second. Musicians refer to this variable as pitch - physicists call it frequency. The frequency variable is referred to in Hertz (Hz) meaning the number of cycles which occur per second. Secondly, we can alter its loudness, this is related to the size, rather than the rapidity, of the oscillation. In broad principle, things which oscillate violently produce loud sounds. This variable is known as the amplitude of the wave.This track also illustrates the possible range of human hearing, which in most adult individuals is limited to about 20Hz to 15kHz.*
Track 3 - Squarewaves at various frequencies* A square wave may be synthesised by an infinite number of sine waves in the manner, f(t) = sin t + 1/3(sin 3t) + 1/5(sin5t) ............. etc. But it's much easier, since the waveform may be thought of in the time domain as switching between two states for equal lengths of time, to arrange a circuit to do just this; in the form known as an astable multivibrator. Just such a circuit was used to generate the sounds on this track.
Track 4 - Piano range; 27.5Hz to 4.19kHz. The relationship between written musical pitch (on a stave) and frequency (in Hz) is illustrated in Fig. 2.5. Note also the annotations on this diagram which indicate the lower and upper frequency extremes of particular instruments. Compare with track 2, notice that the entire musical range is a small subset of the range of human hearing. Remember that the frequency components of the sound produced by each of these instruments extends very much higher than the fundamental tone. Take for instance the highest note on a grand-piano. It's fundamental is about 4.19kHz but the fourth harmonic of this note, which is certainly seen to be present if the sound of this tone is analysed on a spectrum analyser, is well above 16kHz.
Track 5 - The Harmonic Series, up to the twentieth harmonic. Suppose that the vibration of the open string (as shown in Fig. 2.6b), produced the musical note C two octaves below middle C, the subsequent notes follow a distinct and repeatable pattern of musical intervals above the note of the open string. These notes are illustrated in this track. They are termed the harmonic series. A similar pattern is obtainable from exciting the air within a tube as is the case with a pipe organ, recorder, oboe or the clarinet.
Track 6 - Even harmonic series (played two times in the form of a musical chord). Even numbered harmonics are all consonant, their effect is therefore "benign" musically. The same cannot be said for odd harmonics as demonstrated in the next track.
Track 7 - Odd harmonic series (played two times in the form of a "dissonant" chord).
Track 9 - Piano recorded in far-field.
Track 10 - Classical session, crossed-pair, stereo recording. Whilst it’s possible in principle to "mike-up" every instrument within an orchestra and then - with a combination of multi-track and electronic panning - create a stereo picture of the orchestra, this is usually not done. Partly because the technique is very costly and complicated and secondly, because this "multi-miked" technique has not found favour because it fails to provide a faithful representation of the real orchestral experience. As a result, most recordings of orchestras and choirs depend almost exclusively on the application of simple, or "purist" microphone techniques where the majority of the signal that goes on to the master tape is derived from just two (or possibly three) microphones. Surprisingly there are no fixed rules as to how these main microphones should be arranged, although a number of popular deployments have evolved over the years. In this track, the technique of a coincident crossed pair (sometimes referred to - somewhat incorrectly - as Blumlein Pair) is used. Coincident microphone technique encodes positional information by means of angled, directional microphones which capture intensity differences rather than time differences.
Track 11 - Close-miked recording with artificial reverb. Rock and pop vocalists tend to use smaller working distances in order to capture a more intimate, sensual vocal style. Whilst clearly justifiable of artistic grounds, this practice has the incidental disadvantage that dynamic contrasts are often so marked that the signal cannot be adequately recorded and mixed with the instrumental tracks without the use of an electronic dynamic compressor which automatically reduces the dynamic range of the microphone signal (Refer to Tracks 26 to 28.)
Track 13 - Electric organ and Clavinet There are two basic types of electronic organ; divider organs and free-phase organs. The divider type uses a digital top-octave generator (one oscillator for each semitone) and chains of divide-by-two bistables to provide the lower octaves. This has the dual advantage of simplicity and consistent tuning across octaves. However this approach has a number of disadvantages and tends to produce a "sterile" tone disliked by musicians. The alternative is known as a free-phase electronic organ. Theoretically the free-phase organ has a different oscillator for each note of the keyboard. (In the case of the Hammond each oscillator is mechanical.) Hammond's ambitions went far beyond that of reproducing a pipe organ sound and instead aimed at recreating the sounds of other instruments. Their additive synthesis technique involved the analysis of real instrumental sounds and the recreation of these by means of the suitable selection and addition of sine waves generated from the continuous oscillator "bank".
The Clavinet was, commercially and artistically, the most successful keyboard produced by German Company Hohner, who designed it to replicate the sound of a Clavichord.
Track 15 - Slap echo effect (50 - 100mS). The Slap (or Slap-back) echo was first heard in Scotty Moore's chiming lead guitar on the early Elvis' records.
Track 16 - Guitar tape-loop effects. Recordable tape loops originate with the work of Brian Eno and Robert Fripp in the early 1970s, where sounds (in the case of Fripp, usually guitar sounds) are recorded over and over onto a loop of magnetic tape on a tape deck which incorporates the crucial modification that the erase head is disabled and an electrical path provided so that sounds may be re-circulated in the manner of a tape-echo device. The sounds are therefore recorded "on top of one another" and one instrument may create vast, dense, musical structures. Importantly, subsequent signals do not simply add and from an artistic point of view this is extremely valuable because it means, without continually "fuelling" the process, the "sound-scape" gradually dies away. The artist may thereby control the dynamic and tonal "map" of the piece. Nevertheless the control of this process is not comprehensive and many of the results are partially random.
Track 17 - Fuzz or distorted guitar. In a "fuzz" circuit, the guitar signal is applied to a circuit at a sufficient amplitude that it drives the circuit beyond its available voltage swing. The waveform is thus "clipped". For guitarists this effect is amongst their stock-in-trade. It’s now understood, the manner in which the circuit overloads influences the sound timbre.
Track 18 - Wah-wah guitar effect. Wah-wah is a dramatic effect derived from passing the signal from the electric guitar's pickup through a high Q band-pass filter, the frequency of which is adjustable usually by means of the position of a foot-pedal. The player may the use a combination of standard guitar techniques together with associated pedal movements to produce a number of instrumental colours from an almost percussive strumming technique to a lead guitar style (usually in combination with fuzz effect) in which the guitar almost "cries" in a human-like voice.
Track 19 - Pitch-shift effect - Octave down. Pitch shifting is used for a number of aesthetic reasons, the most common being the creation of "instant" harmony. Simple pitch shifters create a constant interval above or below the input signal, like these “harmonies” at the octave.
Track 20 - Octave up.
Track 21 - Pitch-shift, Perfect 4th up; Perfect 5th up. Harmony at a perfect fourth produces only one note which is not present in the original (played) key. However this extra note is the prominent "blue” note of the flattened 7th. It is therefore often acceptable in the context of rock music. For this reason the instant transpositions of perfect-fourth up (or its lower octave equivalent, perfect-fifth down) are the most common transpositions employed in simple pitch shifters (with the exception of octave transpositions).
Track 22 - Flanging guitar. The Beatles' ground-breaking producer, George Martin claims the invention of flanging is due to Ken Townsend, the Abbey Road engineer at the time of Sgt. Pepper's Lonely Hearts Club Band. It came about due to the slight lack of synchronisation between two "locked" tape recorders. (Townsend called the effect ADT). This effect caused various frequency bands to be alternately reinforced and cancelled; imparting on the captured sound a strange, liquidity - a kind of "swooshing, swirling" ring. Of course, such an effect is not practical nowadays using tape recorders, instead electronic delays are used.
Track 23 - Twelve-Bar Blague. A blend on guitar effects used to create a varied ensemble.
Track 24 - Just Leave a Sample Sir! This track demonstrates a sampler used as an effects (FX) device.
Track 25 - Vocoder - Hymn to Aten (First Part) The principal feature of the Vocoder is its two inputs; one for a synthetic sound- source and another for a microphone. Vocoder operation relies on the amplitude envelope of the vocal formants modulating the other musical signal. If this second input is similar to that produced by the lungs and vocal folds, and furthermore is under MIDI control, the Vocoder can be used as an artificially enhanced voice - always in tune and able to sing in perfect harmony with itself! Digitech produce several products of just this type in which they combine this function with intelligent pitch shifting to produce a powerful, versatile vocal processing device. This device was used to produce this track.
Track 26 - Uncompressed guitar - deliberately played with high dynamic contrast. For engineering purposes, it is often desirable to shrink the dynamic range of a signal so as to "squeeze" or compress it into the available channel capacity. The studio device for accomplishing such a feat is called a compressor. When using a compressor, the peak signal levels are reduced in the manner illustrated in the following track.
Track 27 - Compressed guitar. Note that the peaks are reduced but that the gain is not made up. Obviously this would be of little use if the signal (now with compressed dynamic range) was not amplified to ensure the reduced peak values fully exercised the available "swing" of the following circuits. For this reason, a variable gain amplifier stage is placed after the compression circuit to restore the peak signal values to the system's nominal maximum level. This is demonstrated in the following track.
Track 28 - Same effect as Track 27 but with gain made up. Notice that the perceptible effect of the compressor, when adjusted as described, is not so much apparently to reduce the level of the peak signal as to boost the level of the low-level signals; in other words, that the guitar is now apparently louder than in Track 26.
Track 29 - Compressed highly distorted guitar. Unfortunately, compression brings with it the attendant disadvantage that low-level noise - both electrical and acoustic - is boosted along with the wanted signal. Notice the noise floor is unacceptably high. The solution is a primitive expansion circuit known as a noise-gate, the effect of which is to suppress all signals below a given threshold and only "open" in the presence of wanted modulation. The effect of this circuit is illustrated in the next track.
Track 30 - Same effect as Track 29, but illustrating the effect of a noise-gate following the compressor.
Track 32 - Pink noise. (WARNING, due to it’s high energy content, this track is very loud.)
Track 33 - Red noise. (WARNING, due to it’s high energy content, this track is very loud.)
Track 34 - Band-pass filtered noise.
The power of the analogue synthesiser lies in its ability to cause each of its individual components to interact in amazingly complex ways. Fundamental to the whole concept is the voltage controlled oscillator. This may be controlled by a switched ladder of resistances; perhaps by means of a conventional musical keyboard. Or by means of a constantly variable voltage. Thereby providing a sound source with endless portamento like the Ondes Martenot and the Theremin. Alternatively it may be controlled by the output of another oscillator; the resultant being a waveform source frequency modulated by means of another. And perhaps this resultant waveform might be made to modulate a further source! By this means, the generation of very rich waveforms is possible and herein lies the essential concept behind analogue synthesisers. Some examples are given in the following tracks.
Track 35 - Simple near sine-tone patch
Track 36 - Typical analogue bass-synth patch.
Track 37 - Patch with exaggerated action of LFO.
Track 38 - Buzzy string patch sound with ASR generator controlling VCF.
Track 39 - Bass patch, note VCF effect.
Track 40 - Woof sample used to generate novelty backing! Digital sampling systems rely on storing high quality, digital recordings of real sounds and replaying these on demand as shown in this simple example.
Track 41 - Sampled drums. The tough problem sampling incurs is the sheer amount of memory it requires. Sampling is well suited to repetitive sounds (like drums and other percussion instruments) because the sample is mostly made up of a transient followed by a relatively short on-going (sustain) period. As such, it may be used over and over again so that an entire drum track could be built from as few as half-a-dozen samples.
Track 42 - Modern electronic drum samples
Track 43 - Gregorian Chant voice samples. Sampling is great until long, sustained notes are required; like the sounds generated by the orchestral strings or voices. The memory required to store long sustained notes would be impossibly large, so sampled-synthesis systems rely on "looping" to overcome the limitation of an non-infinite memory availability.
Track 44 - Roland SAS synthesised piano. This particular track demonstrates Roland's proprietary Structured Adaptive Synthesis (SAS) which is an eclectic blend of techniques, honed to give the most realistic piano sound possible.
Track 45 - Miller of the Dee. Composite synthesised track used to create slightly frenetic yet, nonetheless, "classical ensemble" sound: Harpsichord - SAS; Recorder and Basoon - LS Sound Synthesis/Wavetable; Strings - Yamaha Dynamic Vector Synthesis.
Track 46 - Christmas Tree. Another composite ensemble with sampled drums; demonstrating a mix with conventional guitar and vocal track. This is a very cost- effective production technique because the majority of the ensemble can be prepared in advanced in a MIDI programming studio, making the acoustic recording stage very simple and fast.
Track 47 - Unprocessed Theremin; some reverb added during recording. The Theremin used on this track has a particularly pure (close to sine-wave) output due to the purity of the RF oscillators and a linear mixer and demodulation stage. The original Theremin had an output nearer to the sound of a violin (i.e. with a large degree of even-harmonic distortion). Waveform distortion is achievable by various means, including reducing the purity of the original RF waveforms or arranging a non-linear detector circuit. However the preferred technique (utilised, for instance, by Bob Moog) is to start with a linear Theremin and to distort the waveform afterwards in the audio domain. Such a technique was used in the following track.
Track 48 - Theremin sound subjected to non-linear distortion post demodulation.
Track 49 - In this track, the Theremin input was used to drive an intelligent harmoniser (Digitech Vocalist Workstation) with the original input supressed. MIDI data was input to the harmoniser to programme the harmonic progression and the Theremin controlled the arpeggiation.
Track 50 - Deep Glissando**; a short piece for unaccompanied Theremin and effects. Effects include pitch-shift (over two octaves), flange, chorus and reverb as well as non-linear distortion, compression and gating.
* These tones are not digitally generated and are not intended for precision measurement.
All tracks on Music Engineering CD disk and this website © Richard Brice 2001. All rights reserved.
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