they reach
more than a few milliseconds, perceived coherence of the source sound is unacceptably
degraded. To reduce the error we use a compensation mechanism. We wait to apply
control data until the largest buffer latency is reached. We thus achieve a lower
interchannel error at the expense of increased latency. This result is better for
performances, because constant delay is less disorienting to the performer than variable
random delays.
Bandwidth is the amount of computation we can spend on each second, which
determines how much oscillators we can resynthesize. In our system, we merely add more
computers to achieve the desired bandwidth requirement.
Future Possibilities
From a technical standpoint, we could easily increase the number of oscillator banks
synthesized on each computer. We only require 1 audio channel of output for
each oscillator bank and several 8 channel DACs are currently on the market.
Optimizing the synthesis routines is also necessary to achieve this performance
improvement.
So far, Netmix has only been controlled by a single performer. It would be a more
idiomatic use of the system to use multiple control sources, such as through
geographically distributed performers or audience-driven multiple sensor input. In the
case of distributed performance, it would be desirable to develop a method for realtime
dissemination of the aggregate audio mix as it being produced (with the minimum
possible latency).
Finally, the system could be expanded to embrace other methods of sound production.
Likely candidates are granular synthesis, processing of stored samples, and processing of
sounds recorded live in performance.
Conclusions
The Netmix audio framework has enabled us to rapidly deploy an experimental live
multi-channel Fourier synthesis model. The framework has some inherent technical
limitations, especially with regard to latency issues. Despite the fact that our
performance is centered on spatial audio, unpredictable packet arrival and deployment
indicate that our system could never be used for precise spatial placement when
deployed on more than one computer.
Given the fact that our interest was in creating spatial diffusion effects which could
not be realized with a stereo speaker setup (in addition to a particular model for
performance control of resynthesis parameters), we are not too concerned with the
temporal indeterminacy due to sound card and network latencies. In addition, the
enveloping involved in Short Time Fourier analysis already blurs the transients such that
latency effects from these sources are somewhat less noticeable. It remains to be seen if
temporal indeterminacy in our system will prove a serious problem when applied to
time-domain synthesis.