Electro-Harmonix Mainframe

Mainframe
Buzz. Beep and bloop. Get high on the lo-fi sounds of “old-school” games, toys and terminals!

The Mainframe provides sample rate reduction ranging from 48kHz to 110Hz. A little background… the sample rate is the number of times per second that a sample or snapshot of an analog signal is taken. For example, CDs (remember them?) had a sample rate of 44.1kHz which means that the original analog signal is sampled 44,100 times per second.

The sample rate defines the frequency range that can be reproduced while maintaining good fidelity. When the sample rate is reduced the quality of the audio is degraded and aliasing occurs. Aliasing means audible artifacts created when higher frequencies are sampled at an inadequate rate and the result is distortion. The Mainframe’s sample rate range is wide enough to take you from sounds that are quite pristine to sounds that are unrecognizable when compared to the input signal.

It also provides bit crushing ranging from 24-bit to 1-bit. What does that mean? Bit crushing is bit depth reduction. Back to our CD example… CDs used a 16-bit bit depth meaning that each of its samples was represented by 16-bits of information. Higher bit depths can accurately represent a greater dynamic range while bit crushing increases the number of sampling errors and creatively degrades the sound to bring us back to those nasty “old school” sounds we love.

The Mainframe’s selectable High/Low/Band-Pass filter lets the user shape the artifacts of the bit crushing and sample rate. Another very cool feature is its Sample Rate Tuning Mode where the pedal analyzes your input signal in real-time and sets the sample rate to match the pitch of your signal, or a set interval above your signal. This allows you to set the sample rate to match the key of a song, or it will continually adjust the sample rate based on what you play!”

Controls:

1. VOL: This knob sets the master output level of the Mainframe.
2. BLEND: This knob blends between the dry guitar signal and the effect signal. As the knob is turned clockwise, the output ranges from completely dry guitar to a fully effected signal with the filter applied.
3. BIT DEPTH: As this knob is turned clockwise, the bit depth of the signal is reduced, producing a distorted, noisy tone.
4. SAMPLE RATE: As this knob is turned clockwise, the sample rate of the signal is reduced, producing a ringing or glitchy tone.
5. FILTER HPF/BPF/LPF Switch: This toggle switch controls the direction of the Mainframe’s filter:

• HPF: High-Pass Filter
  
• BPF: Band-Pass Filter
  
• LPF: Low-Pass Filter

6. FILTER FREQ: This knob controls the frequency of the Mainframe’s filter. As the knob is turned up, the frequency increases. The frequencies cut/passed by the filter vary by the filter type:

• HPF: Frequencies above the FREQ knob setting are passed, frequencies below are cut.
  
• BPF: The FREQ knob controls the center frequency of a pass band. Frequencies above and below this center frequency are cut.
  
• LPF: Frequencies below the FREQ knob setting are passed, frequencies above are cut.

7. FILTER PEAK: This knob controls the resonance of the Mainframe’s filter. Turning this knob clockwise increases the resonance, producing a sharper, more cutting tone.
8. EXP / PRESET Button and Green LED: This button turns expression mode or a saved preset on and off. When the Green LED is lit, expression control is enabled, or the preset is enabled. See pages 6-9 for details on how to save expression settings or a preset.

Specifications:

• Circuit : Digital
  
• Bypass : Buffered Bypass
  
• Audio : Mono
  
• Power Supply : 9.6VDC-200mA power adapter included
  
• Dimensions (in) : 4.5 x 2.75 x 2.1
  
• Current Draw : 90mA