The first is ended, starting the second from scratch

My first Shruthi-1 is finished. It sits now naked on my studio desk among his musical brothers waiting for a shell to be safe in. Everything is ok but the led 5 (as I wrote it won’t lit anymore) and I had some problems during the tuning phase, but everything is resolved.

I would like to share my personal view on tuning:

  • the whole tuning operation is quite quick to complete, but it requires tons of patience and attention (your hears are fundamental, imho) so if you are working for a while take a break or postpone it to tomorrow;
  • during the resonance settings, assumed that you have reached the “no sound” state, be patient because you have to turn the trimpot a while before reaching the “sound” area and then the “louder distorted” area.
  • in the cutoff range tuning turn the lowww trimpot clockwise to get a low pitch and try not to get too much into the “high pitch zone”; in my first tuning I turned the trimpot too much counterclockwise… I don’t know if I get into the instability zone, but it’s clear that what you can get there is negatively affetting the good sound of the shruthi, not worth it.

Another issue I’ve been to: distortion on the whole range of patches/tweaks/everything. I’ve gone crazy for a while fearing a malfunction of my new little brother. Then I realized that it was my system unstable, so nothing was wrong with the Shruthi.

Hoping that this is of help to someone, here is my system: Behringher UMX25 hooked (and powered) via usb to my WinXp pc, Profire 610 audio interface, Shruthi’s midi in connected to Profire’s midi out, Shruthi’s audio output connected to Profire’s line input, I/O and comunication managed via Sonar 6 Producer. There is something wrong in the audio management of (my) Sonar that causes a distortion in the signal coming from the shruthi. If I restart the audio engine the distortion disappear and everything is good. The phenomenon re-occurs in a random way.

This is what. Now I have started my second shruthi-1. The only thing I have right now is the two pcb (digital and SMR4) and nothing else. As I wrote to Olivier this project has involved me so much that I’m using it to learn topics that was pure mystery for me. So I want challenge myself even in the firmware building phase (I’ve never done such a thing before in my life).

So, I’m sourcing parts right now. And here is my first question: I’ve found a shop in Milan selling a clickable encoder that should suits my needs, but it is 12 turns and nor 24. I suppose that a lower number of turns is ok as a higher number (eg. 36) implies problems in the turning rate. Am I wrong? (I hope I was clear)

Thanks for your feedback!

As I said to sync24, the output of the Shruthi is a bit “hot” and might clip a bit on some soundcards when the gain setting is too high. You can fix that by using a smaller resistor on the output op-amp in place of the 68k (for example 22k or 33k).

The 12 steps part works OK - that’s what I used in the first proto. It’s fine for browsing patches and moving through parameters, it’s a bit tedious to use it to adjust parameters with a large range (such as cutoff: 0-127), but for such parameters you have pots anyway. I have never tested 36 steps and I suspect the debouncing code won’t be able to parse the signals correctly, unless the internal switches have very little bounce. Those encoders require a faster decoding rate I cannot afford given the amount of CPU affected to audio rendering.

I don’t think is a matter of resistors or “hot” output. To tell the truth the output volume of the shruthi is ok (maybe a little bit low I would say…) when there is no distortion, so the problem is not in overloading the input of the soundcard. Unless you’re not using a line input but a preamped mic imput: if you play too much with the gain there are many chances to overload the signal.

My distortion appears even if the audio signal is plugged to a line input, the channel volume in Sonar is set to 0dB (no clipping registered) and the output of the audio interface is directly connected to my active monitors (balanced path) which volume is set to 0dB. In these conditions I have to turn the volume knob on the sound card up more than half of its stroke to get a decent volume (not loud but definitely hearable). Under these conditions there is nothing that overloads something (no pun intended!).

I’m still investigating the thing, but I do believe this is something related to the audio engine of my system crashing while sends midi information to Shruthi. I’ll update any news.

Sorry, but I have to be more precise: even when the sound is distorted the overall volume is not so high to let someone think of signal overload!

On my FA-66 the volume of the Shruthi-1 is OK - I had to set up the input gain to half its course. But I tried a M-Audio soundcard on which, even with gain set to 0, the volume of some patches causes clipping (this can be seen in Eaty’s video too). Too bad I haven’t measured this when I captured all those scope traces last wednesday, but I believe the output is above line level.

The Output of the Shruthi with simple bridges for the Out Pot is above “Line” Level (-10dbV Hobbyist…), on my good old MX-8000 i use the Line In with the lowest -40db setting of the Gain Pot while the whole Desk ist set to handle +4dbV as working Level.

Maybe the Op-Amps in muldees soundcard only have ±5V Rails allowing a very low headroom thus distorting at lower levels (the 0db mentioned)? OR a bad example for wrong impedances?

BTW, muldee, anything a brief glimpse more then 0db means instant distortion on a digital System hence it is by definition the max level, better keep some 2-4 db below. There is no headroom on digital Systems, only wrong calibrated (often by purpose by the Manufacturer) Levelmeters.

It may just be an ASIO problem. Assuming your using windows, make sure background processes have priority, and try increasing the buffer size to see if it helps (it will add a little bit of latency too).

Ok, after a few investigations here’s what I can say:

@fcd72: I know the differences between analog and digital 0dB ;). By the way M-Audio says that the maximum input level on Profire 610 line input is +16.1 dBu typical, which means +13,9 dBV that is far higher than the value of Shruthi output. So, once again, I do believe Shruthi is not causing clipping in my system. Please correct me if I am wrong.

I tried different setups, this is what I got:

  • UMX25 disconnected from the pc to operate as a masterkeyboard (powered via power supply), UMX25 midi out to shruthi midi in, shruthi out to Profire line in, Profire hooked to pc via firewire, I/O managed via Profire control panel (no DAW used this time). Audio is perfect, no distortions during quite an hour of test.

  • UMX25 disconnected from the pc to operate as a masterkeyboard (powered via power supply), UMX25 midi out to shruthi midi in, shruthi out to Profire line in, Profire disconnected from the pc to operate in standalone mode (as digital mixer). Again audio is perfect and did not appear any distortion.

I have to test what happens if I make Sonar play a midi sequence sent via Profire midi out to the shruthi, in order to exclude the UMX25. If any distortion appears there’s a ASIO problem with my system (as WillyyDavidK says). Otherwise there’s a conflict between midi messages coming from UMX25 via usb and midi managment of the Profire midi port.

By the way, I opened the thread to ask help on parts sourcing for my second Shruthi-1, but it became something else… what is better to do? Let the thread continue on distortion problems and system analyzing, and I open another thread if I need help with parts sourcing?

Sure, start another thread for parts sourcing questions! I’ve renamed the forum categories to make them more obvious. Hopefully we won’t find too many topics mixed together!