Bass Gear Issue 7 : Page 55to large input level swings as seen in Figs. 3C , 4C , 5C and 6C . This allows a relatively wide dynamic gain of the input signal, despite the unavoidably low iOS ceiling. For instance, the iRig allowed an input signal increase of 560 mVrms between 1% and 20% distortion, with a 60 mVrms increase from 1% to 5% distortion. The Ampkit allowed and input signal increase of 220 mVrms between 1% and 20% distortion, with a 40 mVrms increase from 1% to 5% distortion. The iRiffPort allowed an increase of 720 mVrms between 1% and 20% distortion, with a 158 mVrms increase from 1% to 5% distortion. Figs. 7A , 7B and 7C illustrate the iRig, Ampkit and iRiffPort interfaces in response to a 1Vrms input signal for purposes of comparing overload and phase at a common input level. Correspondingly, Figs. 8A , 8B and 8C illustrate the input compared to the output at the point of clipping of the output signal. Figs. 9A , 9B and 9C illustrate the harmonic spectrum of each interface in response to a 1Vrms, 1 kHz input signal. In the spectral traces herein, the iRig shows relatively stronger odd-order harmonics compared to adjacent even-order harmonics. The plot also shows an extended harmonic spectrum where the odd-order harmonics dominate the even-order harmonics into the higher order. This seems to correspond with the scope plots showing the effects of clipping due to hitting the iOS output ceiling. The Ampkit shows slightly stronger odd-order harmonics compared to adjacent even-order harmonics, but not as exaggerated as the plot for the iRig. The higher order harmonic levels follow a clear, downward step in this spectral plot that tracks well with what we would expect given the typical hard limiting response of the signal to hitting the iOS ceiling. The iRiffPort shows a dramatic roll-off of higher order harmonics. Moreover, the harmonics drop off in a nicely defined slope. These effects track with the earlier observation of asymmetric soft-limiting of the signal. Figs. 10A , 10B and 10C illustrate gain compared to input level. The iRig shows a gain of just under 3.75dB with a slight variance between left and right channels. The input Fig 8B max point of clipping Scope %&& !$%# Fig 7B 1 V rms Scope Fig 7C 1 V rms Scope Fig 8A max point of clipping Scope b;b; Publication List Using a screen reader? Click Here |
