Surround Processor Reviews

The above chart shows the frequency response of the left (aqua), center (green), LFE (red), and left surround (purple) channels at the preamp outputs of the Dolby Digital decoder. The left channel measures –0.17 decibels at 20 hertz and –0.37 dB at 20 kilohertz. The center channel measures –0.16 dB at 20 Hz and –0.36 dB at 20 kHz, and the left surround channel measures –0.24 dB at 20 Hz and –0.34 dB at 20 kHz. The LFE channel, normalized to the level at 40 Hz, is +0.41 dB at 20 Hz, reaches the upper –3dB point at 67 Hz, and reaches the upper –6dB point at 83 Hz.

The analog frequency response, from the CD input to the main output, measures –0.21 dB at 20 Hz and –0.13 dB at 20 kHz in direct mode. Looking at a broader bandwidth, the response measures –0.68 dB at 10 Hz and –0.85 dB at 50 kHz. In modes that involve signal processing, the response is –0.68 dB at 10 Hz, –0.21 dB at 20 Hz, –0.53 dB at 20 kHz, and –63.53 dB at 50 kHz. Response from the multichannel input to the main output measures –1.06 dB at 10 Hz, –0.32 dB at 20 Hz, –0.14 dB at 20 kHz, and –0.77 dB at 50 kHz.

The analog THD+N is less than 0.026% at 1 kHz with a 100-millivolt input and the volume control set to –6. Crosstalk with a 100-mV input was –80.94 dB left to right and –84.22 dB right to left. The signal-to-noise ratio with a 100-mV input from 10 Hz to 24 kHz with "A" weighting was –131.34 dBrA.—MJP

HT Labs Measures: Adcom GFA-7607 Amplifier

This graph shows that the GFA-7607's left amplifier channel, with two channels driving 8-ohm loads, reaches 0.1% distortion at 134.2 watts and 1% distortion at 166.3 watts. Into 4 ohms, the amplifier reaches 0.1% distortion at 253.5 watts and 1% distortion at 303.3 watts. An input level of 101.0 millivolts was required to produce an output of 2.83 volts into an 8-ohm load, indicating an overall gain of 28.95 decibels. With all channels driven into 8-ohm loads, the amp reaches 0.1% distortion at 98.4 watts and 1% distortion at 119.5 watts.

The amplifier's frequency response measures –0.04 dB at 20 hertz and –0.14 dB at 20 kilohertz. Looking at a broader bandwidth, the response measures –0.17 dB at 10 Hz and –0.95 dB at 50 kHz. THD+N from the amplifier was less than 0.004% at 1 kHz when driving 2.83 volts into an 8-ohm load. Crosstalk at 1 kHz driving 2.83 volts into an 8-ohm load was –108.13 dB left to right and –113.63 dB right to left. The signal-to-noise ratio with 2.83 volts driving an 8-ohm load from 10 Hz to 24 kHz with "A" weighting was –116.20 dBrA.—MJP