Music, computer

Before we can discuss the design and architecture of processors for audio DSP tasks, we must discuss the requirements these processors must meet. Then, we will be in a better position to see how the different implementations result in better results. So, we will begin by dividing the requirements into the different tasks. Gordon [Gordon, 1985] has an overview of architecture for computer music circa 1985. 

Numerous commercial instruments were built in the early 1980 s that used asynchronous pitch shifting, including the Fairlight Computer Music Instrument [Roads, 1996], Kurzweil 250 [Byrd and Yavelow, 1986], the E-mu Emulator and Emulator 2 [Massie, 1985], and the New England Digital Synclavier. 

Sample Rate Conversion Techniques. The simplest form of sample rate conversion is called either drop sample tuning or zero order hold interpolator. This technique is the basis for the table lookup phase increment oscillator, well known in computer music [Moore, 1990a],... 

How Many Fractional Phase Register Bits are Needed. The choice of how many bits to make the phase register is an important issue in computer music design. While other authors have covered this issue in relation to traditional sine wave oscillators, there are some subtle differences in the design of sample playback oscillators. Here, the fractional part of the phase register essentially determines how much pitch resolution is available, while the integer part determines how many octaves up the waveform can be transposed (pitch shifted). 

Alles, 1987] Alles, H. G. (1987). A Portable Digital Sound-Synthesis System. In Roads, C. and Strawn, J., editors, Foundations of computer music, pages 244-250. MIT Press. (Also appeared in Computer Music Journal, vol. 1, no. 4, 1977). 

Cook, 1992] Cook, P. R. (1992). A meta-wind-instrument physical model, and a meta-controller for real time performance control. In Proc. 1992 Int. Computer Music Conf, San Jose, pages 273-276. Computer Music Association. 

Dolson, 1986] Dolson, M. (1986). The phase vocoder A tutorial. Computer Music Journal, 10(4) 14-27. 

Massie, 1985] Massie, D. (1985). The Emulator II computer music environment. 

Proc. of International Computer Music Conference, pages 111-113. 

Moorer, 1981] Moorer, J. A. (1981). Synthesizers I Have Known and Loved. Computer Music Journal, 5(1) 4—12. 

Roads, 1996] Roads, C. (1996). The Computer Music Tutorial. MIT Press, Cambridge, Massachusetts. 

Roads and Strawn, 1985] Roads, C. and Strawn, J., editors (1985). Foundations of Computer Music MIT Press, Cambridge, MA. 

Rocchesso and Smith, 1994] Rocchesso, D. and Smith, J. O. (1994). Circulant feedback delay networks for sound synthesis and processing . In Proc. Int. Computer Music Conf, pages 378-381. 

Smith, 1985] Smith, J. O. (1985). A new approach to digital reverberation using closed waveguide networks. In Proc. 1985 Int. Computer Music Conf, Vancouver, pages 47-53. Computer Music Association. Also available in [Smith, 1987]. 

Smith, 1996] Smith, J. O. (1996). Physical modeling synthesis update. Computer Music J., 20(2) 44-56. Available online at http //www-ccrma.stanford.edu/ jos/. 

Stautner and Puckette, 1982] Stautner, J. and Puckette, M. (1982). Designing multichannel reverberators . Computer Music Journal, 6(l) 52-65. 

Truax, 1994] Truax, B. (1994). Discovering inner complexity Time shifting and transposition with a real-time granulation technique. Computer Music J., 18(2) 38-48. 

Wawrzynek, 1989] Wawrzynek, J. (1989). VLSI Models for Real-time Music Synthesis. In Mathews, M. and Pierce, J., editors, Current Directions in Computer Music Research, pages 113-148. MIT Press. 

Sample rate conversion. All of the synchronous pitch shifting techniques essentially involve sample rate conversion techniques. The theory and practice of sample rate conversion has received extensive coverage in many excellent texts and articles, but it is illuminating to compare the computer music perspective with the traditional sample rate conversion literature. Insights from the sample rate conversion literature provide insights to the computer music perspective, and vice versa. 

Drop sample tuning can introduce significant artifacts from changing the pitch of a waveform. This method originated in the design of early computer music oscillators... 

Figure 8.10 The traditional ADSR amplitude envelope used in electronic and computer music, with the looping region shown.

In the field of computer music, it is customary to use simple piecewise linear functions for functions other than signals at the audio sampling rate, e.g., for amplitude envelopes, FM-index functions, and so on [Roads and Strawn, 1985, Roads, 1989]. Along these lines, good initial results were obtained using the simplified qualitatively chosen table... 

Alles, 1977] Alles, H. G. (1977). A Modular Approach to Building Large Digital Synthesis Systems. Computer Music Journal, 1(4) 10-13. 

Arfib and Delprat, 1993] Arfib, D. and Delprat, N. (1993). Musical transformations using the modification of time-frequency images. Computer Music J., 17(2) 66—72. 

Barriere et al., 1989] Barriere, J.-B., Freed, A., Baisnee, P.-F, and Baudot, M.-D. (1989). A Digital Signal Multiprocessor and its Musical Application. In Proc. of the 15th Inti. Computer Music Conference. Computer Music Association. 

Chowning, 1973] Chowning, J. (1973). The synthesis of complex audio spectra by means of frequency modulation. Journal of the Audio Engineering Society, 21(7) 526-534. (Reprinted in Roads and Strawn, Foundations of Computer Music,... 

Gordon, 1985] Gordon, J. W. (1985). System Architectures for Computer Music. 

Kahrs and Killian, 1992] Kahrs, M. and Killian, T. (1992). Gnot Music A Flexible Workstation for Orchestral Synthesis. Computer Music Journal, 16(3) 48-56. 

---