STUDIO

discussion of DSP is that audio products whichuse it will only really be limited in their powerby the amount of processing capacity and thespeed of operation. In the face of such flexibility,manufacturers will be in the difficult position ofhaving to decide just where to stop in thedevelopment of new products, as it will be onlytoo easy to carry on adding new features. Suchdevelopments imply that the audio industry willbecome very much like the computer industry, inthat the latest DSP hardware will dictate thespeed at which operations can be performed (andthus the sort of audio applications which arerealistic in realtime) whilst audio designers willbe market researchers or software engineers.It would not be unreasonable to assume that themixer as we know it will change considerably.There is already evidence of this in Yamaha'sDMP7, in that the digital nature of the systemhas resulted in the incorporation of effects andautomation as well as the traditional equalisationand faders. Likewise, some manufacturers whichare researching the matter see the role of themixer broadening in its scope to provide a widerange of facilities which had not previously beenoffered. This might spell the end of large racks ofoutboard processing equipment.Psycho -acousticprocessingEven more interesting than digital mixing is thepotential that DSP offers for simulating real -lifeaural experiences which are entirely based onlevel and time differences between the ears. If itwere possible to define a number of time delayand level -related templates which corresponded toparticular aural situations, then it might befeasible to superimpose these onto dry- recordedaudio material to convince the listener that hewas actually experiencing the simulated situation.Such a suggestion is surprisingly not particularlyfar -fetched, as will be shown below.Psycho- acoustic research could play animportant role in the development of DSP -basedaudio products. Few people have so far consideredprocessing sound sources with this aspect ofperception in mind, as it is one of the moreesoteric and lesser- understood areas of audio, yetthe potential is enormous. The amount of effortbeing invested in this area of research by certainEuropean companies, in collaboration withuniversities, is quite surprising, and it is clearthat some serious money is being poured intoprojects related to a whole new generation ofaudio processing.So far, most of the aural effects that can besimulated by such systems require the listener towear headphones, as the principles are based onthose of binaural perception, but it can only be amatter of time before it becomes possible tocompensate for the effects of loudspeakers androom. Using time delay and spectral shaping it ispossible to position sounds anywhere around thehead of the listener, and in any type of acousticsurrounding.Acoustic designconsultancyLooking at what has just been said about psycho -acoustic simulation it can be seen that such aprocessor would be the ideal tool for the acousticdesigner. Wearing headphones and experimentingwith different types of wall- covering and shapes ofroom, the designer could know what a room wasgoing to sound like before it was constructed! Thesoftware of the system would interpret thedrawings of the room, the different surfaces, andtheir reflective characteristics in terms of delayedreflections at different times and amplitudes, aswell as calculating the standing wave modepositions and amplitudes. The designer couldposition himself anywhere in the room and listento the effect of changing a particular aspect of theconstruction or treatment with sound sources indifferent places. Again, we are simply talkingThe Creative Audio Processorfrom AKGabout digital audio signals being delayed,multiplied and added to each other to achieve thedesired effect; the limitation being in the numberof these operations that can be carried out in agiven period of time, as audio is essentially arealtime phenomenon.It is possible to imagine the time when not onlycould an architect lead his client through acomputer model of a new building to see what itwould look like (this is already possible), he couldalso give an impression of what each room wouldsound like! The implications of changing adimension or a surface covering could beconsidered both aurally and visually.A real productAs an example of the sort of work being done it isinteresting to look at a commercial product,embodying a number of these principles. AKG'sCreative Audio Processor (CAP340M) is based on anumber of time delay modules and an audioprocessing computer, under control of a HewlettPackard HP -300. The audio processor is a fastcomputer optimised for the crunching of audiodata, handling it in 32 -bit floating -point form atan instruction rate far higher than that of mostmodern desktop or mini computers. The userinterface is graphic, with a mouse.Presently, the product is at the `what do youwant to do with it ?' stage, where virtuallyanything is possible and a number of suggestionsare offered. The following are some examples ofprogrammes currently used:Digital mixing: A number of audio inputs areprovided and the mixer panel can be user -configured to provide such functions as delay ofeach input (to align the arrivals from multiplemicrophones), elevation of the sound source (apsycho -acoustic effect) and position of source. Thenumber of channels depends on the number ofinput and output modules chosen, and also theamount of processing installed.In very friendly fashion, the processing of eachinput can be adjusted not by entering numbersbut by moving the positions of `microphones' inmowrelation to the listening position using a mousewith the graphic display. These inputs are thenfiltered and delayed according to the effect oftheir position. Going further, it is possible tosimulate the use of a co- incident or binaural pairby using spot microphones and delaying /filteringthem according to the characteristics of therequired pair at a particular point.Room simulation: Dimensions of a virtual roommay be entered, and the surface coverings of theroom defined from a library of common materials.The room is then graphically displayed, and asound source can be placed within the `room' witha binaural `microphone' positioned to listen to theeffect of changes in sound source position or roomcharacteristics.Methods and costWith audio computers using DSP in such ways asthose described above, the way in which operatorsand consultants work may be changed. Thepositioning of multiple microphones for arecording may be less important, and it may notbe necessary to have four loudspeakers in thehome to reproduce surround sound. The designerof a new concert hall may be more sure that itwill sound as he intends, and he will be able todemonstrate this to people before it is too late.Currently the cost of DSP hardware is high, andthe cost of software is even higher. Many man -years are required to cover the sort of researchrequired in audio processing, psycho- acoustics, andmarket requirements. It is likely to be the end ofthe century before DSP is widespread in the audioindustry, as only then will the initial mistakeshave been made and the cost of processing comedown to a reasonable level. It will also take thatlong for companies to learn tricks of the trade.One should not forget the Japanese in this, asthey have already shown what is possible interms of DSP at low cost (Yamaha DMP -7 andRoland digital equalisers. These products indicatethat large -scale products cannot be too far away,and without an unreachable price tag.181