brief explanation on options beyond the basic model...
If you do not have a high quality Microphone Pre-Amplifier available you might choose to have one included into the VOC design. The Pre-Amp module basically amplifies up to 60 dB with a S/N ration over 80 dB. Amplification can be set with the GAIN control between 2 and 1000x (6....60dB) in combination with a Amp-Range switch (2...100x and 2---1000x) to let you apply any input signal.
If you want this option you may think about what kind of input plugs you need, Phantom power for Mic's and/or
Compressor / Expander
Using a Compressor / Expander improves the overall quality of the Vocoder effect on a dynamic level. You might need it to improve non stable voice dynamics and/or to improve Signal to Noise ratio. If you already have a Compressor / Expander module you do have an advantage above this option. This is because the mass produced Compressor / Expander modules nowadays have great possibilities in treating both input and output signal. nevertheless, you might want a dedicated and specifically designed unit included into your Vocoder design. In this case both Compressor and Expander do have a bypass switch to generate certain 'effects'. You even might have them available externally by way of added in and outputs.
Although balancing the output sections to a final mixture, an Evelope Depth Control on each channel opens a new horizon. 24 control pots are add and as a secondary option you might like to have a LED indication for each channel.
Besides the 'normal' Vocoder effect and the plug-in presets, you can create different patches with a patch bay to generate alternative Vocoder effect. This means that you change the control order of the 24 channels with patch cables. This all to alter the normal control setup to modify specific sounds. The patch (sound) that you find by experimenting with the Patch Bay can be fixated with a plug-in preset card. They are easy to make yourself with standard available components which you can buy at your local electronics store. Simply change the plug-in card to generate a complete different effect.
Patch Preset bank
As you can understand, using plug-in cards to change the patch presets also can be inconvenient in a studio situation wherein guests have to experiment with the Vocoder standard effects. Therefore you may choose to also have a turn switch included to easily switch between the standard Vocoder effects. This option you would take together with the Patch Card option. You then can switch between normal / external patch bay, patch card, 6 fixated standard effects and 4 variations on these standard effect.
Response speed control
The response time of the base version is fast. This means that the VOICE input dynamics are transferred to the CARRIER (through the envelope followers and VCA's) without smoothing. This to have the dynamic details in the VOICE also represented in the Vocoder output effect.
An option is to have control over this so called response speed to be able to smooth these detailed dynamic changes in the VOICE signal. It makes the Vocoder effect less natural (when related to the human voice) but opens a horizon for certain effects.
This response speed control can be of a 'single' type: to control all the 24 channels at once. But, you also could wish to have such a speed control for each section (5x) or even for each channel - depending on the refinement you desire.
Multiple Voice & Carrier inputs
Instead of having a single Voice input and two Carrier inputs, you also may choose to have a Voice and Carrier input on each section (2x5). This would allows you to patch for each section a different input and thus extend your range of effects and even to split-up the Vocoder into independent Vocoder effect machines (with respect to the frequencies band range for each section).
Multiple section outputs
Having an individual output for each section would allow you to send sections to other effect modules and also to independently mix them out on your mixing table. It is interesting to think about having an Vocoder effect with a certain effect for example only on the middle section, another effect on the low section(s) and again another effect on the high section(s).
Stereo end mix output
Instead of a MONO mixed output (6 section joined in a single mix) you also may choose for a stereo mixed output.
There are several configurations to mix the 6 sections to stereo. For example: The Low section fully to the left, the LowMid section fully to the right, the MID section in the middle, The MidHigh at 75% to the right and at last the High section at 75% to the left.