User`s guide

E-Prime User’s Guide
Appendix A: Timing Test Results
Page A-18
4. Audio Output Latency – This test checks the delay between when an audio output is initiated
to the time until a signal is detected at the output of the audio card. During this test an audio
signal detector circuit is plugged into the output jack of the audio card. When an audio signal is
detected, a pulse is generated on a TTL line connected to the TS. The ES prepares an audio
stimulus for output, sends a start signal to the TS, and then immediately initiates playback. The
TS watches for the audio detect signal from the interface hardware, timestamps the event, and
reports the time between the start and detect signals. All tests were run on the same machine,
and the operating system (Windows 95a for this test set) was reinstalled prior to installing each
card and its drivers. Each card tested was a PCI card except for the Sound Blaster 16, which
was a legacy ISA bus card.
The data below shows that audio performance can vary widely depending on the audio card,
driver, and bus type being used. Desktop audio systems are primarily designed to meet the
needs of the computer gaming market. This market has very soft real-time constraints (e.g.,
delays on the order of 1-3 screen refreshes are not typically a concern or even noticed by a game
player). The tests indicate that with the appropriate sound card, you can achieve low and
consistent playback latency (e.g., the Sound Blaster Live card showed very consistent
performance with an average delay of <1.9ms with a 0.5ms standard deviation and a maximum
delay of 3ms). The Sound Blaster 16 had bad performance with high variability (e.g., standard
deviation of 19ms with a maximum delay of 89ms). In general, ISA sound cards do not perform
as well as PCI cards under the Windows environment, and we do not recommend them for time
critical audio experiments. The other poor performer in the test was the AOPEN AW200 card,
which was a very low cost ($12) generic PCI card. We recommend investing in a quality, name
brand, PCI audio card.
In general, most of the current generation, name-brand PCI audio cards and drivers can provide
an average playback latency of <1 screen refresh in E-Prime.
AUDIO PLAYBACK DELAY BY AUDIO CARD TYPE
Audio Card Model
Sound
Blaster Live
(PCI)
Sound
Blaster 128
(PCI)
Turtle Beach
Santa Cruz
(PCI)
AOPEN
AW200
(PCI)
Sound
Blaster 16
(ISA)
Average of DELAY
1.88 8.04 3.32 24.48 29.68
StdDev of DELAY
0.526 1.791 0.557 12.370 19.054
Min of DELAY
1 5 3 15 14
Max of DELAY
3 11 5 77 89
N (Num of Trials)
25 25 25 25 25