Freed, Adrian adrian@cnmat.berkeley.edu
Chaudhary, Amar amar@bmrc.berkeley.edu
Davila, Brian davila@cnmat.berkeley.edu
Center for New Music and Audio Technologies
1750 Arch Street
Berkeley, CA 94709
USA
phone (510) 643-9990, fax (510) 642-7918
ICMC 1997 Poster Proposal
Keywords: Latency, Real-time, Measurement, Benchmark, Operating Systems
Content Area: Realtime systems
There is increasing interest in using PC and Workstation platforms in reactive sound synthesis and processing applications. However, few operating systems were designed to deliver real-time performance and vendors generally don't guarantee or even specify the performance to be expected from operating systems products. Considerable experimentation is required with each operating system to achieve musically reasonable results.
The ability to measure I/O latencies represents a major technical difficulty in achieving reliable real-time performance for musical applications and is the subject of this paper. The problem is to synchronously log stimulus events like those from MIDI, ethernet, USB, Firewire, audio input, etc., and subsequent changes in processed or synthesized audio sound streams.
Conventional instrumentation capable of such logging is expensive and challenging to configure. The solution we present records events using an affordable and readily available multichannel digital audio recorder, such as a DAT or ADAT recorder. The challenge is to convert high bandwidth, event related signals to frequencies below the Nyquist rate of the recorder. This is easily achieved by recording an audio reference that is amplitude modulated with a monostable triggered by positive and negative edges which are derived from the event source. The time constant of the monostable is the temporal uncertainty of the end of an event and can be set to provide adequate accuracy when logging at audio rates.
Presentation of the logging system and associated analysis tools will be followed by results from application of this latency test harness to PC, Macintosh and SGI computer systems.