Voltages on the SSP

This topic discusses how CV and audio levels are handled by the SSP.

Physical Input/Output jacks

The input and output jacks are capable of -5v to +5v aka -/+5v. This is true for both audio and cv signals (which are treated identically).

beyond these limits voltages are safe, but will be clipped. e.g. sending in 7v , the SSP will treat as 7v, -5.5v = -5v

Since the SSP allows both CV and audio, these IO jacks do NOT have any DC offset removal. it is assumed modules within the SSP will remove offsets if required for audio signals. (if you use PMIX, then this will remove DC offsets by default)

Calibration

High quality converters are used, but there will also be some variation due to components used. this can mean voltages are slightly 'off'. Usually this is NOT an issue, however, it is important when we are dealing with pitch signals, which use v/oct, since slight variations will cause things ot be out of tune.

there are two ways to handle this issue: a) use a quantizer (e.g. SHQ) the voltages are usually close enough, that a quanitzer will nicely 'snap' onto the correct voltage.

b) manually alter scale/offset if you use something like DATA, you can see the voltages, and so use the scale and offset built into the SSP network screen to compensate. the INP module also allows for these to be altered via gain/offset. usually, very small amounts are required for this.

Audio signals

It is worth remembering the SSP is assuming input and outputs signals are eurorack level, so -/+5v. this is VERY 'hot' for equipement operating at line level- this will distort badly for outputs, and be very quite on inputs.

you can handle this in hardware , either by using IO eurorack modules, or things like physical mixers will often have PAD setting to allow gain to be reduced to useable levls.

however, you can also handle in 'software' on the SSP :) on inputs, you will want to use the GAIN parameter to amplify the signal, if this is not enough, you can also 'scale' the output on the network screen.

on output, simply attenuate the signal before output (to around 20%) using the scale function on the network screen. or simply turn down level in PMIX.

INP/OUT modules

the INP and OUT modules are used to convert the physical voltages into the 'virtual signal' used between SSP modules. this means we go from talking -5v to +5v , to -1.0 to 1.0 ... see below for more discussion on this.

bare in mind, when you send a signal to the OUT module, do not exceed -1/+1 as it WILL clip and sound distorted.

Virtual signal

we know that the SSP is receiving -/+5v , and the INP/OUT modules convert this into a virtual signal thats in the range -1.0 to +1.0. using -1.0 to 1.0 is the convention in DSP (digital signal processing). most of the time we dont see this within the SSP , and you can probably think of its still as -/5v, but there are occasions its useful to know this.

also when we talk of -1.0 to + 1.0, this is the 'normal range', and is the limits shown on the scopes on the network page. however, the signal can quite happily exceed these ranges internally within the SSP. the times to be careful (so look for clipping on those scopes) is:

• INP/OUT physical outputs will simply clip, and sound horrible if you go beyond +/- , so always attenuate beforehand
• other modules some DSP will expect a signal to be in this range, so may do nasty things outside of it ;)

pitch

So, if we have v/oct... how does that get translated to -/+1

very simply... as 5v = 1 , we can see that 0.2 = 1v = 1 octave.

USB input/outputs

When you connect the SSP to a computer as an audio interface we have 24 channels of usb input and outputs. The first 16 usb inputs map to the 16 physical inputs, and the first 8 usb outputs replicate the 8 physical outputs. this is quite handy, as it means patches built for physical world can easily be use in a computer setup e.g. using VCV rack.

this USB io is also not DC coupled... so allows for both CV and Audio. if you are sending audio, you may want to use a DC offset removal 'tool' on your computer (available in VCV and most DAWs)

obviously USB is digital, so we have no worries about things like calibration, what the SSP sends, the computer gets! just like the SSP uses 'virtual signal' in the range -1.0 to 1.0 (see below)

not: as with all digtial protocols there will be some latency.

pitch again ;)

however, it should be notes there is NO STANDARD for what -1.0/+1.0 represents, its just considered the 'full range' in the case of audio, this is not really an issue...

but if you want to mix 'pitch cv' then it can raise a complication.... what is full range? as stated the SSP, like many digital modules is -/+5v, but other eurorack modules are -/+10v , or some other amount :)

This can cause a little confusion when integrating pitch CV on your computer eg. with VCV or a DAW. since it has no idea what 1 means, is it 5v or 10v, and so conversly how to track pitch.

The good news is.. this is a well known issue. so, software when it accepts CV input (or outputs CV) will allow you to specify a range. therefore for the SSP set it to 5v , and it'll work.

if the software does not support this... and you can hear its wrong (e.g. its assuming 10v). simply divide (or mulitply if outputing) the value by two. its all digital so is 100% precise ;)