"control signal" sound?

Hi Shruthi users,

I assembled my Shruthi-1 last week and all seems to work ok ( it sounds really, really good) , but there’s something I’m not sure about …

When I press and hold a key on my MIDI keyboard ( When I Set the 2 oscillators to none and all the filters parameters to 0 cut. ,res., env. and lfo. ) I can hear a low “electric sound” through the speakers…

…Is this sound normal ? or it is something regarding :
…with a bad tuning?
…with the use of PWM for the oscillators and control signals?

Is this a normal “control signal” sound/noise?

I found in an other post that the control signals maybe is not clean enough…

Can anybody help me?
Thanks in advance

could you maybe post a sample of this sound?
it’s hard to tell just from the description.

The signal to noise ratio is around 75dB so there should be a small amount of digital noise when the volume is cranked up. The fact that this noise is dependent on what you play is not very normal.

Does this noise get louder or can you hear a click at the note start when you play with all the oscillators set to none? If so you might have to trim the DC pot.

Hi community!

… well, i´m a beginner on understanding how a synth works… :slight_smile: … i ´ll try to explain me:

rosch/: Sorry, i´m out of home, i´ll try to post it this night…

pichenettes/: The noise is clear, without a “click” …I can hear this sound when , for example, I press and release a key and the envelope release time set to 127 is still working…

Hi !,

I trimed the Shruthi three more times, and everytime I can hear the same “control signal noise” ,
You can find an example on the next upload:

( I can hear this sound at the background of many configurations…)

Thanks in advance

A .wav file would help a lot. Soundcloud does all kind of compression, and I can’t even download the file for loading it in sonic visualizer.

Just tried to reproduce this and yes, its total normal behavior of the SMR-4 Filter (i think you are referring to that one).

Let me introduce you to a Phenomena that was known in ancient times as Noise
As the Shruthi is a real digital analog/digital hybrid Synthesizer it produces real analog and digital noise - at about 55db if i can trust my Console. So if you crank up the gain and try to find some noise you will as soon the VCA opens. This ist normal if you would hear nothing your Shruthi would be dead. If some noise (that is shurely covered by the awesome good sounding signal, isn’t it??) a problem for you try a VA Plugin - Synth. You can open as many instances in your DAW and hear only silence but badly its all virtual.

Digitally a zero is a zero is a zero - silence! But there are no Zeros in the real world hence the universe seems to be more of an analog Kind as far as our concept of the World shows.

Historical note: The PPG Wave series is known to produce tons of digital hiss and noise above 15khz - and thats part of the Magic. If you filter that away most of the Magic of the PPG is gone…

Note#2: My Waldorf MicroWave 1 produces similar noises when the OSC switched off and the VCA opens…

What I measured some time ago was around -66dB.

The power supply might also be noisy - some very cheap wall warts expect each device to be fitted with noise filters from hell and giant 1mF caps. If you have a battery clip with a DC jack, try powering it with batteries to rule out the power supply.

I did the measurements again.

VCA closed: 80.1dB
VCA opened: 68.1dB

Which is close to the 12-bits sweet spot (72dB).

JX-8p: 58dB. SH-101 (on batteries): 53dB. The JX-8p noise is “structured”, with periodic “thumps” that are just 37dB below the signal level - I did the measurement outside the thumps.

If you want me to do the check on your unit (I don’t know at which level the sound you posted is recorded), please send me a .wav file recorded at 24 bits on a decent soundcard, which contains a note, some silence after it, and the same note with the oscillators switched off. We’ll know for sure if you have a problem with your unit or discovering the combined imperfections of analogue and simple, DIY design.

Oh and did you change the LEDs? If you put high power LEDs (white or blue), they might pull the supply a bit everytime they blink, so on the modulations or sequencer page you’ll “hear” the blinking. Straight out of a 74hc* is certainly not the right way of driving “power” LEDs anyway.

Hi community!

Fcd72/: thanks for your notes… yes, I think it is logical for analog/digital hybrid Synthesizer ( Shruthi is my first Synth) the problem is that i can hear the noise in the background of many sounds… (…maybe i´m a little bit perfectionist :-P)

pichenettes/: …no, the leds are the standard ones of the kit…,
Ok, i´ll try to power the unit with a battery clip and I ´ll test it again.

Olivier, thanks for your work: for a beginner like me, I think that your DIY Shruthi, at the same time as a real musical instrument, is an amazing way to discover how a synth works.


Can you make a recording in which there’s a normal preset sound, then you cut the oscillators to zero, then play a note to let the background noise flow through the VCA? Maybe there are swapped resistor values somewhere and the signal is not amplified as loud as it should be at some point - degrading the SNR.

Go and get a JX8-P while they are cheap. The noise the Chorus emits all the time even when not playing a note is really Musical :wink: I smile everytime when i hear a new recording if there is some kind of Noise in the beginning or silent passages as it shows that at least a real analog Console was used… so a bit of Noise is good, as it adds a musical, human touch to everything. No noise most of the times is just sterile.

P.S.: I can sample the JX8-P-chorus noise and send you a Disk in EMU-Format - will add a human touch to everything :wink:

Hi fcd72!

…uhm…It sounds really well… I´ll ask Noel for the JX8… :stuck_out_tongue:

…it was impossible for me to do it last week.
Now I think the audio quality is better than the “soundcloud” file… you can see the settings on the video too:


What do you think?