Digital Sound Synthesis and Usability Testing

Digital Sound Synthesis and Usability Testing

Overview of analogue/digital synthesizers and their input in the music industry

An essential issue in the researches of new media happens to be to investigate and clarify the connection between technological development and cultural revolutions. In this case, digital technology has usually been seen as the single most significant tool in the design of numerous of today's new cultural terminologies. In media that is heavily reliant on computers and relative software, like blogs, the case becomes even more palpable; however, digital technologies may also be associated with changes in more conventional media like film, music as well as literature. Many comprehend the emergence of those novel expressions due to new technology conquering the restrictions of the earlier versions of the analogue format of media. After this argument, you might end up expecting that producing inventive documents in a brand new millennium will be the consequence of an electronic revolution that had left prior formats of analogue technologies obsolete. Modern culture has generally an optimistic attitude towards the beginning of digital technology, considering it being an enhancement on its analogue precursors. In this specific article I wish to have a closer look at these assumptions by creating a step-by-step investigation to the role of digital technology in the assembly of popular music in the world today, in anticipation of expressing something more specific concerning the association that exists between technology and cultural terminologies (Barlindhaug, 2007).

"From a certain point-of-view, it clearly looks like digital production tools are the dominating force in the western cultural expressions of today. The 80s and 90s produced a large range of digital hardware, culminating in a growing software and computer industry. Through the application of software, computers can be turned into powerful tools for the production of documents. Most literature describes the introduction and development of digital media as providing great freedom in manipulating information, both for consumers and producers. For most of us, "digital" equals "new and better." To a certain degree this is also true of musical production. Diverse software has been designed to make computers function as tools for both recording and producing sound. One important trend in this regard is the integration of a range of so-called software synthesizers into your music production. These are programs that function like real-life machines, but existing only in the software environment of the computer. A good example of this is "Reason," made by the Swedish company Propellerheads Software, a sound production tool with the graphic and functional appearance of a physical rack. Here the user can add units like drum machines, mixers and synthesizers, and on the backside of the rack you can connect the units together using colorful cables" (As cited in Barlindhaug, 2007).

All aspects and structures are very lifelike, but at exactly the same time remain acutely virtual. "Reason" is excellent in that it's an entire production environment, while all the computer software synthesizers are created to function as part of larger tools and software as plug-ins. These plug-ins in many cases are replicating mechanisms that are also available as hardware. In the beginning this may appear to be a prime and commendable case of the innovative progress of digital media knowledge. However, many aspects simply don't accumulate that easily. To begin with: Why do we would like computer software that functions like a real machine? In the end, making wordprocessing computer software work the same as a typewriter wouldn't seem very novel. However, this is very much indeed the structure in music assembly. Also, with the overabundance of computer software accessible, why are corporations prepared to exhaust U.S.$1,400 on e-bay for a little battery-based musical device from the year 1982 onwards, when you are able obtain a computer software version free of charge? Academics have conceptualized a number of theories unfolding the influence of digital media, but how of use are these when attempting to explain what's happening in a particular domain like music production? (Barlindhaug, 2007)

When attempting to scrutinize electronic music on the basis of conventional media notions, it is vital to indicate that there's a significant big dissimilarity in how theorists, practitioners and musicians recognize media knowledge and tools. This big difference also details the reasons behind why media theories can't explain what's going on in music production. Conventionally, theorists think about media as something broadcasting a note or functioning while the material basis continues on with this message. There's a consensus that this material basis imposes restrictions and influences what's communicated, and by doing so affects the end result. However, regarding the electronic music, the media is constituted with a longer assembly sequence that expand farther than the instantaneous material basis. Even though the material basis for the music that is being produced may be the same, what eventually classifies its overall artistic appeal is what media was utilized in its previous assembly. In musical terms, technology plays an important role as a structure that is necessary for production, and not just as a way for storage and distribution. It's also essential to indicate that a lot of the technology utilized in music production contains media that easily could be recognized to be used both as storage and producer of content. Due to musicians' concentrate on the mechanisms, the separation that is present between the analogue and digital technological structures is, for the musician maybe not so much so about the technical evolution aspect, but instead it remains to be a question of artistic appeal or aesthetics. The development of educational and artistic notion is, in fact, in these instances a direct result the utilization of the technology, not just of its technical evolution. Based on this, the material facet of technology becomes a completely independent entity whose importance isn't based solely upon its virtual originality. For the concern that currently exists in the view of the technological determinists, I believe many theorists have ignored these aspects of media progression and technology. When placed under stricter inspection, the execution of digital technology can therefore result in have a significantly different and varying consequence than had been initially believed or anticipated (Barlindhaug, 2007).

Advantages of digital synthesizers (Virtual instruments):

Error Recognition

Adjustment in Broadcast

Data Density Construction and Adjustment

Digital Synthesis Techniques

Digital subtractive synthesis, which has also been known as the virtual analogue synthesis, describes computational techniques that duplicate or reproduce the sound generation axioms of analogue synthesizers that were originally developed back in the early 1960s and 1970s. The fundamental principle in subtractive synthesis was first to create an indication with a dynamic ethereal content, after which to sift that particular content or signal attained, the time-varying resonant filter was used successfully.

"Virtual analogue synthesis became a popular and commercial term in about 1995, when Clavia introduced the Nord Lead 1 synthesizer, which was marketed as an analogue-sounding digital synthesizer that uses no samples. Instead, all sounds were generated by simulating analogue subtractive synthesis. Previously, the Roland D-50 synthesizer of the late 1980s worked in a similar way although it contained sampled sounds. An early example of an attempt to design a digital synthesizer that sounds analogue was Synergy" (Kaplan, 1981 as cited in Huovilainen and Valimaki, 2006).

Why digital subtractive synthesis is experiencing a higher demand ratio than that which is usually comprehended is that duplicating or reproducing analogue tools or electronics using the digital processing isn't as straightforward or simple as it might seem or come across to the lay man. One difficulty is aliasing brought on by assortment of analogue waveforms which have sharp boundaries The continuum of such waveforms carry on infinitely elevated levels, and the signals hence may not be band-limited. Yet another intricacy is that analogue filters don't obey simple linear notions. With elevated signal degrees, they create alteration or warp signals. This doesn't obviously or logically surface in digital processing, however it should be planned, calculated, structured as well as executed very purposely, see for instance, the methods used in the studies conducted by Huovilainen in his 2003 research as well as Rossum in an earlier research conducted in the year 1992.

Figure 1: obtained from Huovilainen and Valimaki, 2006

Subtractive Synthesis

The electronic music designs first initiated in the mid 1960s by Robert A. Moog (Moog, 1965) are perhaps one of the more essential innovations in music evolution of technology, both in technical and aesthetic aspects. A couple of years later, his company established products and services where in fact the various structures, designs and modules, for example oscillators, filters, and amplifiers, were built-into just one portable unit. Subtractive synthesis was the primary principle utilized in these instruments. 'Minimoog' was one of the more popular analogue synthesizers in 1970s (as cited in Huovilainen and Valimaki, 2006).

The Prophet 5 synthesizer was another breakthrough that was first initiated as part of the Sequential Circuits back in the year 1979. It had features like microprocessor controlled electronics; however it continues to be used as an analogue synthesizer. Its block diagram shown in Fig. 1 (below) is today a vintage exemplary case of the subtractive synthesis principle. It offers two oscillators, a resonant low-pass filter, and two envelope generators (ADSR). There are always a handful of alternative waveforms available as well as a noise source (as cited in Huovilainen and Valimaki, 2006).

Figure 1: taken from Huovilainen and Valimaki, 2006

Digital Oscillators

The jagged boundaries of geometric waveforms used nowadays in digital oscillators, like the saw-tooth or the square wave, result in the creation of assumptions, as these kinds of signals aren't band-limited. Three various classes of techniques are recognized to avoid this issue:

1. Band-limited techniques that produce harmonics only beneath the Nyquist boundary, for example additive synthesis and its own variants, e. g., wavetable synthesis and the discrete summation formulae (as cited in Huovilainen and Valimaki, 2006);

2. Quasi-band-limited techniques by which aliasing is small and its own level could be regulated or altered by design to truly save computational expenses, for example in the BLIT [9] and the minBLEP [1] methods (as cited in Huovilainen and Valimaki, 2006);

3. Alias-suppressing techniques by which it is established that various assumptions will surface and be created but an effort is built to attenuate it adequately (as cited in Huovilainen and Valimaki, 2006).

In a recent study conducted by Huovilainen and Valimaki (2006) the researchers concentrate on the 3rd group of techniques. They highlighted two particular approaches here which were: the distortion and filtering of sine waves, which the termed in their paper is Lane's method (Lane et al., 1997) as well as the differentiated parabolic waveform (DPW) (as cited in Valimaki, 2005). They discussed the latter in the following way:

"DPW algorithm: The simplest version of the DPW algorithm [11] generates the saw-tooth waveform in four stages, as illustrated in Fig. 2: First generate the trivial saw-tooth waveform using a modulo counter, then raise the waveform to the second power, differentiate the signal with a first difference filter with transfer function H (z) = 1 -- z -- 1, and, finally, scale the obtained waveform by factor c = f/(4f), where f is the fundamental frequency of the saw-tooth signal and fs is the sampling rate. The waveform produced by the modulo counter resembles the saw-tooth waveform, as seen in Fig. 3(a), but it sounds badly distorted. The reason is that its spectrum decays slowly, about 6 dB per octave. When it is sampled, the spectral components above the Nyquist limit are mirrored down to the audible frequencies. This is clearly seen in Fig. 4(a), where the desired harmonics are indicated by circles and the rest of the peaks are aliased images" (as cited in Huovilainen and Valimaki, 2006).

Figure 2: obtained from Huovilainen and Valimaki, 2006

Figure 3: obtained from Huovilainen and Valimaki, 2006

Figure 4: obtained from Huovilainen and Valimaki, 2006

Figure 5: obtained from Huovilainen and Valimaki, 2006

The researchers further asserted that raising the signal to the 2nd power modifies the waveform such that it now includes bits of parabola, see Fig. 3(b). The spectral range of this waveform decays about 12 dB per octave, and for this reason aliasing is suppressed in Fig. 4(b) [11]. Finally, when the piecewise parabolic signal is differentiated and scaled, the signal again appears like the saw-tooth waveform, see Fig. 3(b), however the aliased components are suppressed, as observed in Fig. 4(c) (as cited in Huovilainen and Valimaki, 2006).

They also write that another problem is that at high frequencies the amount of aliased components is near to that of the harmonics. This might lead in some instances to beating. An answer of avoid this would be to replace the differentiator using its averaged version HD (z) = 1 - z-2 = (1 + z-1) (1 - z-1). The resulting waveform and spectrum are shown in Fig. 5. It sometimes appears that in the discrete-time waveform in Fig. 5(a) the transitions from the most value (near +1) to the minimum value (near -1) are smoother than in Fig. 3(c). The corresponding spectrum, see Fig. 5(b), decays faster at high frequencies than that in Fig. 4(c) (as cited in Huovilainen and Valimaki, 2006).

Improved Moog Model: Non-Linear Method

Huovilainen is promoting a better model that designs the ladder trip by placing the nonlinearities within the one-pole segments (2004). He asserts that this enhanced design far more intimately imitates or reflects the typical resonance and it is effective at self-oscillation. A disadvantage may be the importance of five hyperbolic tangent (tanh) function assessments done as per sample and oversampling by factor two at the very least (Huovilainen, 2004).

An alternative solution and extended model is shown in figure 7 (taken from Huovilainen and Valimaki, 2006). The embedded nonlinearities inside each and every segment is replaced with a single nonlinearity in the reaction sphere, hence greatly reducing the computational expenditures of the filter. We now have used the tanh utility for the nonlinearity, but any efficiently saturating function can be utilized. There's a big difference in the resonance set alongside the full nonlinear Moog filter model, but this particular design chosen can emulate all the activities and mannerism, for example self-oscillation. Its output can, in addition, be constantly restricted.

The brand new and innovative design also includes two additional improvements. The standard Moog filter and comparable cascaded one-pole filters suffer with declining the pass-band gain while the quality and tone/sound is elevated, since the resonance is fashioned with a worldwide negative feedback. If a few of the contribution is subtracted from the reactive or response signal before the sound degree are multiplied, the pass-band gain change could be controlled (Curtis Electromusic Specialties, 1984). A value of just 1.0 for the comp parameter keeps the pass-band gain constant. This, on the other hand, creates a sizable increase and elevation of the output amplitude while the resonance is also simultaneously risen. To help keep the entire intensity roughly steady, comp must be rested at 0.5 producing a 6 dB pass-band gain reduction at the most resonance (when compared with a 12 dB reduction in the initial Moog model).

Figure 7: taken from Huovilainen and Valimaki, 2006

Yet another improvement may be the accumulation of numerous frequency response modes form original 24 dB/oct lowpass mode. This is often easily attained by mixing the patient section outputs with differing weights. The idea was initially established in the Oberheim Xpander and Matrix-12 synthesizers (Oberheim, 1984 as cited in Huovilainen and Valimaki, 2006), however the researchers asserts that "it was not widely used due to a large number of required components and the need for precision resistors. Accurate mixing is trivial in the digital domain, and a large number of different low-pass, band-pass, high-pass, and notch filter responses and their combinations can be realized. The response can be morphed between these modes by changing the coefficients at runtime, thus allowing interesting modulation possibilities" (Huovilainen and Valimaki, 2006).

Digital subtractive synthesis is really a modern approach by which aspects of analogue music synthesizers are designed with the utilization of the signal processing techniques. So far, in this paper, we have highlighted the use of the digital oscillators and resonant filtering algorithms as discussed in numerous relevant research studies. It is important to note here that the DPW oscillator algorithm creates a saw-tooth waveform estimate that has paid down aliasing and assumptions with regards to the trivial saw-tooth waveform (i.e., the modulo counter output). This new method has become the simplest of use technique for this function, because only the trivial saw-tooth is very simple, however it is practically useless because of its heavy aliasing (Huovilainen and Valimaki, 2006).

"The new nonlinear model of the Moog ladder filter is based on a cascade of four one-pole filters and a feedback loop that contains a memory-less nonlinearity. The proposed new Moog filter structure has nice advantages, such as a smaller computational cost than that of a recently proposed nonlinear filter structure, the decoupling of the cutoff frequency and the resonance parameters, and the possibility to obtain various types of filter responses by selecting a weighted sum of different output points. The proposed methods allow the synthesis of retro sounds with modern signal processing techniques" (Huovilainen and Valimaki, 2006).

Usability testing

In addition to meeting the rising opportunities, there are lots of concrete remunerations for procuring companies from superior usability of interactive structures. Work efficiency and organization are elevated when utilizing IT systems with high-quality usability, and you will find a smaller number of 'user errors'; less preparation of staff is needed to facilitate valuable and efficient make utilization of the structure, users tend to be more satisfied, and there might be decrease in the overall percentage of staff turnover. You will find profits and advantages both for users and producers for the reason that less sustenance and certification is needed. Such benefits could be enumerated, measured, and integrated right into a production case for requesting usability production in system expansion (Macleod, 1994). Karat (1993) gives abundant examples.

An additional incentive for businesses marketing or utilizing the information systems structures in Europe may be the European Directive 90/270/EEC (CEC, 1990) concerning use display screens, that has been employed in national law in associate nations. This is primarily concerned with the tangible ergonomics of workstations, but presents quite a few interesting demands when it comes to the expectations of high-end usability: "software should be ideal for the duty... computer software should be simple to use... The systems ought to exhibit all facts and database information in a particular and user-friendly layout and at a velocity which can be adopted easily by the users ... [and] the axioms of computer software ergonomics should be applied" (Macleod, 1994).

The scope of usability

Usability professionals usually meet people who think usability could be put into something simply by providing a particular type of interface. However, usability is a lot deeper compared to superficial options that come with the consumer interface. While interface features are essential in assisting shape the usability of the machine, simply having a good group of widgets doesn't guarantee usability -- interface components are the inspiration for constructing areas of something, with the purpose of acceptably presenting to the consumer obviously understandable information and feedback, and providing a suitable way of entering data and commands easily and effectively. Adding, for instance, a graphical interface -- even one with easy-to-use objects -- might not provide a system a suitable degree of usability unless the look fulfills the expanded usability requirements. Majority of the style guides recognize this; for instance, the Open Look graphical interface application style recommendations (SUN Microsystems, 1990): "The presence of those graphical elements does maybe not guarantee good application design; that depends upon you."

What then is usability? It may be looked at as a quality that is beyond plainly useful, it is an excellent degree of the communication between user and system. Now, that's where usability is harder to reason about logically as opposed to several other qualities of computer software products and services. Usability is determined by the faculties of the consumer along with the computer software. Something might have exceptional quality useful for a lot of and low quality useful for the others. For instance, a graphical interface might have straightforward, well planned menus -- which beginners and new users can investigate and utilize productively and securely -- but can be quite frustrating for skilled, recurrent users since it lacks keyboard shortcuts (Macleod, 1994).

Usability also depends upon the particular tasks people wish to perform. For instance, a database might have sufficient usability for recurring data entry responsibilities, but poor usability for creating reports. Usability can also end up suffering from environmental facets, from physical influences such as for example incident light and sounds, to organizational facets such as for example interruptions in mid task (Macleod, 1994).

Ergo we must think about usability when it comes to the caliber of utilization of an interactive structure by its (anticipated or targeted) users for the completion of specific tasks, aims and activities particularly when considering the corporate work structure. This view is reflected within an up-and-coming international standard, ISO 9241-11 (ISO 1993b), which supplies assistance with assessing usability when it comes to "the effectiveness, efficiency and satisfaction with which specified users can achieve specified goals in particular environments."

Design, testing and improvement

"It is not the intention here to prescribe how to design usable systems. Some valuable relevant general texts are available (e.g. Nielsen, 1993; Norman, 1987); and copious guidance is provided in the various parts of ISO 9241 (ISO, 1993a). But it is worth considering several pieces of advice which are widely accepted. Firstly, follow good high-level design principles. A very clearly and concisely expressed set of such principles can be found in the opening pages of 'Human Interface Guidelines: The Apple Desktop Interface' (Apple Computer, 1987). Further principles, with examples of their use, are given in ISO 9241-10 (ISO 1993c). Secondly, if appropriate follow a specific style guide, which should enable the developer to provide consistency of interaction style, both within the application and with other applications familiar to the users. Thirdly, and most importantly, involve users in the process of design and development. To develop IT systems which adequately meet user needs requires the participation of (intended) users, along with other stakeholders, from requirements capture to acceptance testing or market release" (as cited in Macleod, 1994).

Prior to the application of an IT structure, many people are inexperienced at envisioning from its specification how it'll look, feel and function, and how appropriately the look will meet users' requirements. There's ample evidence from systems developed utilizing the one-shot development techniques that even talented designers acting under superior individual facets axioms can't foresee how users will respond to an applied structure. This isn't to reject the worthiness of early professional participation from usability specialists, who are able to draw on the knowledge and connection with how models can fulfill user requirements, or the utilization of checklists (e. g. Ravden and Johnson, 1989) and heuristic assessments (Nielsen and Molich, 1990; Nielsen, 1992). On the other hand, the first and continuing utilization of mock-ups and prototypes to achieve user feedback encourage positive yet critical analysis and recommendations for improvement directly associated with user needs, which may be fed back to development iteratively. Essentially, this introduces user-based evaluation to the development process. Required for its success would be the range of representative users, and responsibilities which are directly related to the proposed system utilization (Macleod, 1994).

Evaluation, validity and context

Means of usability evaluation might have various purposes: for instance, to shape design (or redesign) to meet up user needs; to recognize and diagnose issues; to judge implementation (for comparative assessment with other designs and systems and for acceptance testing). The information collected might be qualitative (for assessment of facets highly relevant to usability) or quantitative (measures which indicate usability). Observe that quantitative data don't of necessity provide a valid indication of the amount of usability. For instance, many methods to usability evaluation focus specifically on user issues. Reducing issues is really a desirable aim, and is extremely valuable for improving usability, but unless the issues are vigilantly graded for severity, an issue count could be a misleading indicator of overall usability. Most users prefer to encounter a few trivial issues than the usual single catastrophic problem which in turn causes task failure. Evaluation could be applied at different stages throughout development: at specification (analytic and expert techniques); whenever a mock-up or prototype can be obtained (expert and user-based techniques); and after implementation (user-based techniques). Generally, the sooner evaluation could be applied; the more cost-effective it is, as long as it is valid (Macleod, 1994).

As has been detailed above, the usability of a structure is dependent upon not just the faculties of the merchandise itself, but additionally the faculties of users, the errands they fulfill and their work surroundings. Together, these can be defined as the 'context of use' of the merchandise. For an assessment to be economically applicable, the background facets which bear on the assessment (the 'context of evaluation') must imitate the proposed context useful.