The 31 buttons on the front panel are divided into six sections. They are: Parametric EQ, Dynamics Processing, Delay, Output, System, and Presets. The parametric EQ of the 601 is quite versatile. This is a 3-band equalizer. Bands 1 and 3 can be switched to shelving EQ. All three bands can cover the entire frequency range of the 601's EQ which happens to be from 31Hz to 21.11kHz. Each band can be adjusted from +18dB to -50dB. The bandwidth of each EQ band can be set from .05 octaves to 3 octaves. Any of the three bands can be turned on or off independently of the others by pressing the BP button for that band. When active, the red LED in the center of that band's BP button illuminates. When bypassed, the LED is out. When flashing, that band can be edited with the three EQ editing buttons -- Frequency, Level, and Width - and the large data wheel. Pressing Frequency lets you use the wheel to set the center frequency of the selected band. Pressing Level enables adjustment of the amount of boost or cut. Pressing the Width button lets you modify the bandwidth of the selected band.
The next section of the front panel is devoted to the Dynamics Processor of the 601. This section includes the de-esser, dynamic noise reduction, downward expander, compressor and AGC. There is a button for each of these and four other buttons used to select adjustable parameters of each of the five dynamics processors. These four buttons are Attack, Release, Frequency/Ratio, and Threshold. Pressing the NR button toggles the noise reduction between active and inactive or "out" as the display reads. When active, the Frequency and Threshold buttons become active and are used to adjust the "resting" frequency of the NR. The Threshold button accesses two threshold settings used to set the NR for the appropriate input. The 601's dynamic noise reduction circuitry uses a variable frequency low-pass filter to perform single-ended noise reduction.
Pressing the DS button activates the 601's de-esser. (The de-esser and noise reduction blocks cannot be used simultaneously.) When the de-esser is active, the Threshold becomes the only active parameter button. The Threshold setting sets the level where the de-essing actually takes place.
Pressing Expander activates the downward expander, and all parameter buttons become active -- Attack, Release, Ratio and Threshold. Attack time is adjustable between 0.1ms and 10 seconds. The release time can be set between 100ms and 10 seconds. The expansion ratio is adjustable from 1:0 (out) to 1:8.
While the expander reduces its gain for signal below the threshold, the compressor reduces its gain when audio is above the set threshold. As with the expander, the compressor provides adjustments of attack time, release time, ratio and threshold. The ratio is adjustable from 1:1 (out) to 10:1.
The AGC block cannot be used while the compressor is active and vice versa. Pressing the AGC button activates the AGC and all four parameter buttons. The ratio is adjustable from 1:1 to 4:1.
Thresholds on the NR and de-essing blocks are adjustable from 35dB to 0dB, and on the expander, compressor, and AGC from -100dB to 0dB. A note in the manual explains that "All of the dynamics blocks use a threshold parameter. Unlike analog processors that you may be familiar with, each of the threshold settings in the 601 reference to digital clipping (full-scale) rather than to some nominal signal level (like 0dBu). This means that you may not be able to directly translate threshold settings that you are familiar with from the analog world to the digital world." This is of no concern to most, but if you're one who sets up dynamics processing by the numbers rather than your ears, this is worth noting.
The next section of the 601's front panel provides six buttons devoted to the Delay block. This is a dual delay with feedback and delay-time modulation. Though quite simple compared to more elaborate delay algorithms found in digital effects boxes, the 601 provides quite a few nifty effects with this simple delay block. Modulation of the delay time enables such effects as chorusing and flanging and a very short delay simulates small room reverb. The Mix button sets the mix between the delayed signal and the direct signal. The Delay button is used to set the amount of delay. Pressing the button toggles between delay 1, delay 2, and dual delay modes. In each mode, the current delay time is shown in the display. Maximum delay is 330ms. The Feedback button sets the amount of feedback as well as the phase of the feedback. The Filter button activates the lowpass filter with a range from 600 to 18kHz. The Rate button sets the frequency or rate of the modulation generators, and the Depth buttons sets the modulation depth. These parameters provide several effects more commonly associated with digital effects processors. In fact, some of the effects were as good as those found on boxes designed more towards special effects. You get ping-pong delays, echoes with changing pitches, PA system effects, and even automatic panning achieved by modulating the output levels with the oscillator in the delay section.
The next section of the front panel is the Output section which has two buttons. The Bypass button does as you'd expect. However, only the DSP is disabled; the signal still passes through the converters. The Level/Pan button is used to set the output level and left/right panning of the 601.