Surround Processor Reviews

Analog frequency response in Stereo mode:
–0.36 dB at 10 Hz; –0.12 dB at 20 Hz
–0.07 dB at 20 kHz; –57.74 dB at 50 kHz

Analog frequency response with signal processing:
–0.36 dB at 10 Hz; –0.12 dB at 20 Hz
–0.07 dB at 20 kHz; –58.08 dB at 50 kHz

The above chart shows the frequency response of the left (aqua), center (green), LFE (blue), and left surround (red) channels at the preamp outputs of the Dolby Digital decoder. The left channel measures –0.03 decibels at 20 hertz and –0.11 dB at 20 kilohertz. The center channel measures –0.04 dB at 20 Hz and –0.07 dB at 20 kHz, and the left surround channel measures –0.03 dB at 20 Hz and –0.11 dB at 20 kHz. The LFE channel, normalized to the level at 40 Hz, is +0.11 dB at 20 Hz, reaches the upper –3-dB point at 96 Hz, and reaches the upper –6-dB point at 117 Hz.

Response from the multichannel input to the main output measures –0.16 dB at 10 Hz, –0.04 dB at 20 Hz, –0.03 dB at 20 kHz, and –0.24 dB at 50 kHz. The analog THD+N is less than 0.021% at 1 kHz with

a 100-millivolt input and the volume control set to +2.0. Crosstalk with a 100-mV input was –95.13 dB left to right and –95.71 dB right to left. The signal-to-noise ratio with a 100-mV input from 10 Hz to 24 kHz with "A" weighting was –121.07 dBrA.—MJP

HT Labs Measures: NAD M25 Amplifier

All channels driven continuously into 8-ohm loads:
0.1% distortion at 194.3 watts
1% distortion at 230.7 watts

Frequency response:
–0.23 dB at 10 Hz; –0.07 dB at 20 Hz
–0.19 dB at 20 kHz; –1.09 dB at 50 kHz

This graph shows that the M25's left amplifier channel, with two channels driving 8-ohm loads, reaches 0.1% distortion at 207.7 watts and 1% distortion at 259.5 watts. Into 4 ohms, the amplifier reaches 0.1% distortion at 394.3 watts and 1% distortion at 484.6 watts. An input level of 98.30 millivolts was required to produce an output of 2.83 volts into an 8-ohm load with the level controls set to maximum, indicating an overall gain of +29.18 decibels.

THD+N from the amplifier was less than 0.002% 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 –109.73 dB left to right and –104.01 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 –112.67 dBrA.—MJP