Torture Pulse
Torture Pulse
For this test we changed over from SmaartLive mode to recording mode. A series of non-frequency-specific square pulses were fed to the DUT and recorded onto my IBM ThinkPad T30's line level minijack inputs. A few cuts were introduced into the DUT in order to ensure that our EQ was doing some work and not idling with filters disabled at their detent positions. In the photo you can see the NEI 2711 (out of production) displaying the specified EQ settings of 315Hz -3dB, 400 -6, 500 -6 and 630Hz -3dB. One channel of the ThinkPad was fed EQ'ed pulses and the other was fed straight pulses. This allows for the subtraction of the ThinkPad's response from the EQ'ed DUT response, though some argument can be made that the EQ'ed signal will hit the ThinkPad a little differently making it respond in a non-linear fashion between its Left and Right channels. At least all DUTs were treated the exact same way, so intelligent comparisons are still possible.
At the top of this graph you can see the original pulses taken from the first of two groupings. They are perfectly square with every non-zero sample at the same value -- about 70% of maximum level. This what they looked like coming in to the EQ getting tested. Next level down shows what the computer thinks of as an ideal response given the EQ settings specified. At the bottom you can see the so-called ideal response subtracted from the original pulses.
Analyzing the resulting recordings allows us to look at several things. We can check to see if any device takes too much time to ramp up to full level after a period of silence, we can compare ski-jump tops of EQ'ed pulses and we can see how a device responds to a sudden absence of signal. A further inspection of these audio files might yield additional information.