A little more detail on SSP INP/OUT and DAW use case

Now that my SSP has returned from the dead…I have a question.

You mention in your Wiki (Latency · TheTechnobear/SSP Wiki · GitHub) the following interesting tidbits (emphasis mine):

“ok, now truth is the above was a bit overly complicated …we could also use. PLTS → OUT : 3/4 INP 1/2 → OUT 1/2 now connected QPAS to inputs 1/2…the reason I used 5/6 in first example is beginners often incorrectly assume there is some kind of magic connection between inputs and outputs … there is NOT , INP 1/2 in no way relates to OUT 1/2.”


“something else we have not discussed here is the relationship between the SSP audio interface IO and how they relate to INP and OUT modules and flexibility there. but all I’ll say for now, is the ‘default’ mapping, that maps physical to virtual io ports has a bit of flexibility. and also whilst I used 1/2 above for simplicity… Id often use the higher numbers (above 16) so I dont mix physical IO with virtual IO… unless thats what I actually want”

In using the SSP as an audio interface between my DAW (Logic Pro) and Eurorack, is there a way to use the same channel numbers for input and output? In Logic, you can use the I/O plug-in to create a virtual send/return loop through the SSP. But if I use the same USB channels to send and return on the SSP, I get feedback. I’m currently using alternate channels (i.e., OUT Ch 1 & 2, IN Ch 3 & 4); otherwise, feedback ensues. I like the idea you mention above about using higher numbers (> 16) to avoid mixing physical and virtual I/O. Can you expand a little more on how to configure SSP’s INP and OUT to make that happen and avoid the feedback?


Sorry, I don’t understand your question? or issue?

sorry, thats not true… as I stated above…

if you are getting feedback its because you are taking feeding the output back into the input…

on the SSP side its all pretty logical, the inputs and outputs are completely distinct from one another.

the only thing that might confuse some, is that the physical IO overlaps the USB io by default !!
so if you output on usb ch 1-2, this AND the physical IN 1/2 will come in (summed) on IN:1 IN:2

as I said, this is why sometimes I use the higher USB channels, since these dont have a physical equivalent…

although that default physical mapping is also damn useful in many use cases … so I can see why its the default.


If this diagram represents the desired set up, then what settings configure the INP and OUT modules to pass audio to/from the DAW (via USB) without causing feedback between the modules? Should INP not be linked to OUT? Does audio pass through to the USB I/O without having to link the INP and OUT modules?

I think your missing something, but Im still not quite sure what :wink:
indeed there is no reason, in the above case for you to connect IN to OUT… what are you trying to achieve?

lets start with the simplest use-case… and build up from there?!

lets use the SSP as a send effect for a daw…

IN ->CLDS → OUT , set CLDS to 100% mix (as we are going to use as a send effect.)

in your DAW
create a send effect, that outputs to SSP : out 1/2, and receives audio from SSP in 1/2

and this should work … AS LONG as you also dont try to output the main audio to SSP 1/2 !
(which would create a feedback loop!)

ok, so thats and effect using SSP internal modules…

what if you want to go to an external eurorack module?

this is where , you have to stop and think a bit !
(and probably where you are getting confused, given your above diagram…)

if you output on USB 1/2 this will DIRECTLY INP 1/2, but you cannot go to OUT 1/2 to get to they physical outputs eurorack module…
as whilst out 1/2 would go to your module, it’ll also send to usb 1/2

so you’d end up with the dry signal back on usb…
but worst…

if you then send your eurorack module to in 1/2, its ‘return output’ is going to be summed with the usb 1/2 input… (remember: as I said in first post… physical + usb ports are summed!)
which you have just connected to out 1/2 , which goes to both usb 1/2 out AND your eurorack module on 1/2
hence the feedback…

as, I said, once you remember that that usb and physical io are overlapped ( * ), it becomes quite logical that you cannot do this.

so what to do?

well the easiest thing to do is, (as suggested previously), use the higher USB port numbers which do NOT represent physical ports !

so get your DAW to output on USB 17/18, and receive on USB 17/18
now on the SSP…

INP 17/18 → OUT 1/2 (to send to eurorack 1/2)
IN 1/2 (from eurorack) → OUT 17/18

viola, all works, no feedback…

now this is only ONE way to do it.
there are other ways… e.g. you will notice INP allows you to map the physical ports to virtual ports.
but honestly, unless you are feeling confident with the above, just keep the default mapping, as its one less thing to remember.

one other trick to remember… you can have multiple INP/OUT modules.
this can make things a little less confusing for beginners, as you can kind of use one INP/OUT pair for the usb side, and another for the physical side.
(note: port assignment is identical… it just might feel a little tidier when your are unclear whats going on)

( * ) ok, its tempting for someone seeing this, to say , why the hell do the usb / physical ports ‘overlap’
… and for sure in this scenario its not wanted.
BUT there are a ton of cases (particularly when wanting to eurorack audio) where this is REALLY useful, and this default overlapping makes it very quick and simple.

I guess, the long n’ short is… the reason we have 24 in/out usb channels is to use them…
so get out of the habit of thinking of using only the lowest channels.
and rather, lean towards using lower channels for this ‘overlap’ and higher channels where you dont want this overlap.

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I followed your advice and dedicated USB channels 15-16 as a return, and it all works fine as long as I don’t use the physical INP 15-16 (which overlays the dedicated USB return channel). I prefer having the SSP set to 96k to match the studio’s system clock, so that naturally limits the SSP to 16 in/out USP channels. I’m OK with that.

I found that the INP needs to be connected to the OUT for the DAW to “see” the 16 incoming USB audio channels:

If I don’t connect the INP to OUT, nothing shows up in the right-hand column of the network menu for the INP module. Conversely, if I disable the INP to OUT connection, no INP channels are available for the OUT module in its network menu. With the INP-OUT connected, levels appear on the SSP USB input channels 13-14 and 15-16 in Logic:

Hopes this all makes sense.

PS. It looks like I still have some DC showing up on CH 2. I’ll need to have the dual op-amp replaced on that channel. All the others look fine.

which is why I said 17/18, not 15/16 :wink:

as, I said, this all depends what you are doing…

if you are trying to connect inputs to outputs then, of course, you you need to connect (come of) them, but there are other scenarios where this is completely unnecessary e.g. as I showed when using CLDS, or say if you are using a mixer…

but really the point of my post was NOT specifics, rather to illustrate the ‘issues’ in a more general sense. since you were not clear what you were trying to do, so hard to know why you were having issues with patching.

… as I say, lots of options with the SSP, so you have think it thru a bit at times, to find the best solution to what you need… theres not ‘one right way’

anyway hopefully now you understand the basics, you can get to where you need to.

yeah, that looks excessive to me… though you can use an offset for now, to limit the issue.
(Im assuming that is unconnected… since many eurorack modules introduce offsets even with no signal)
it may not be the opamp but rather the components biasing it… something slightly out of tolerance, or perhaps a cold joint… even that offset doesnt take much. hope you can get it sorted.

Should we be nulling (short) the physical inputs on the SSP in this use case?