SPEM - Serial Parallel Effects Mixer

SPEM (Serial Parallel Effects Mixer) is like few products in one :

  • 4 channel Serial Effects Mixer,

  • 4 channel Parallel Effects Mixer,

  • 4 channel Instruments Mixer,

with Peak, RMS or Dynamic Range Metering and three time windows.

SPEM helps you to control input/output volume however SPEM can also help your creativity, with a simple switch you can change the routing connections from Serial to Parallel or Parallel to Serial. There is a channel selector that can be CV controlled, you can choose one channel at a time, be adventurous and put an LFO on it and continuously switch between the channels.

The user interface has been optimized to have all necessary functionalities in a 1U rack, even when folded, key controls are still available.

Serial Mode

In serial routing mode, the goal is to help volume leveling between each stage of the effect chain, works seamlessly inline or the mastering chain.

Main input audio signal goes to the Channel 1 outputs, connected to an effect of your choice. This effect sends back the audio signal to the channel 1 inputs, which sends it to the Channel 2 outputs. And so on for the Channel 3 and 4. For each channel you can measure levels and adjust volume, pans and polarity.

If a channel is not plugged, or is muted, then it is bypassed.

After crossing all channels, the global dry/wet mixer lets you mix the wet audio signal with the main input audio signal. You can adjust the main output audio level with the output volume knob and measure it with the output meters.

You can change channels sequence without changing connections on back panel.

Parallel Mode

In parallel routing mode, the goal is to help volume leveling parallel effects. It can also be used as a powerful mixer of four audio inputs.

SPEM takes incoming main audio signal, splits it into four audio signals assigned to the four channels outputs. Each channel sends audio to an effect and gets the returned signal back. You can measure levels and adjust volume, pans and polarity.

At the end, SPEM merges all channels returned audio signals. You can adjust the main output audio level or mix the merged audio signal with the dry main input audio signal.

Common features

  • serial or parallel routing selector,

  • special function named Solo Gain that increases volume with a gain depending on the number of soloed channels,

  • volume control on input and output main audio,

  • D+W option that lets control the dry and wet audio input or/and output volume,

  • global dry/wet mixer,

  • three mixer modes : Linear, Constant Power and Gentle Taper,

  • global bypass button,

  • channel selector,

  • LEDs and digital meters with three modes : peak, RMS or Dynamic Range; and three time windows : 0.4 s, 3 s, 10 s,

  • hold display to show max,

  • one main audio signal input,

  • four audio channels with send and return audio connectors,

  • one main audio signal output,

  • one thru audio output to help cascading,

  • CV for volume knobs,

  • CV for pan knobs,

  • CV for channel selector with options : channel 1 to channel 4/All, unipolar/bipolar signal.

Channel features

  • volume or cross-fade in Mixer Mode,

  • independent pan left and pan right controllers, or cross-fade in Mixer Mode,

  • pre option lets you drive (volume, pans, polarity) sent (outputs) signals. If pre is off, volume, pans and polarity act on returned (inputs) signals only,

  • Mixer Mode : cross-fade volume and pans with dry signal in parallel mode or previous channel in serial mode. Mixer Mode is only available without pre option,

  • polarity inversion,

  • mute,

  • solo,

  • low lighted blue LED indicates that a channel is plugged in (inputs or outputs),

  • high lighted blue LED indicates that a channel is selected,

  • red LED indicates that a channel is muted in solo mode (another channel is soloed).

The meters have a special damper function to have a readable peak value and a quick response.

The controls (volume, cross-fade, pans, polarity, mute, solo, select, mixer) have a smooth change in about 10 ms (except polarity change for which a cross-fade occurs in 64 samples). So you will never hear cracks or pops when you mute a channel !

SPEM is optimized to reduce CPU load.


Don't connect audio in main input, choose parallel routing and SPEM is running like a simple mixer.

You can combine two SPEM, one with main input + channels outputs plugged with pre option on, and another with only channels inputs and main output plugged. This is a tip to have both controls on inputs and outputs.

You can use a similar tip if you want less channels by plugging outputs of a channel into inputs of another channel.