Analog soul and the CV attenuators

One reason why analog synthesizers are so popular in these modern days in my opinion is the fact that they don’t work every time like expected or surprise you in a way like a VST instrument won’t. Attenuators (or potentiometer also called) for example work in a mechanical way. In consequence every unit acts a little bit different and will change their behavior over time regardless the high industrialized production quality. You can easily realize that by using the Main Tune knob: it has a midway indent which isn’t precise enough to land on the same frequency again once you turned it. In my humble opinion this indent makes not much sense on this pot but since you have three additional knobs to tune the two oscillators it isn’t a problem at all. There are eight attenuators with midway indent altogether used in the Synvoiz and some of them can influence the sound while sitting in their neutral position because of these little imperfections. The best illustration I found so far is the CV 1 pot at the filter section. Default the LFO 1 is routed there. I recorded a standing bass sound with no modulation dialed in – CV 1 in center position.

While recording this I turned the LFO 1 frequency slowly up and you can hear that very clear in a change of harmonic content. The solution for this is pretty simple.  Just plug a spare cable into the CV 1 socket. Now the sounds stays stable:

As long as the source of prerouted modulation is only slowly changing in time the variations in sound might appeal to most users. If you have trouble to understand a certain aspect of your sound and suspect an ongoing “secret” modulation just plug a cable into the according socket to bypass the routing.

Starting position

You got the unit, turn it on, connect the audio and midi cable and don’t hear anything while pressing keys on your keyboard? Here are some first hints to get started:

There are four locations where the output volume can be influenced. The master volume doesn’t need any explanation – just turn it on. At the envelope section (the faders) you will find in the top left corner one called BIAS which basically bypasses the whole VCA section. The fader underneath called CV controls the envelope amount going into the VCA. In the filter section you have two input controls. For the start tune only the IN 1 into middle position*. Now comes the tricky part – the extra VCA section in the middle of the oscillators. When the MIX control is in middle position and the little black knobs around it are all turned counterclockwise you should hear nothing. The MIX control blends in OSC 1 or 2. If you want to hear both at the same time use the BIAS controls over it. Now you should hear something. Turn the knobs listen whats happening and try out some stuff. Happy tweaking!

* The filter input can be overdriven pretty easily. The IN 2 is the ring modulated signal of both VCAs.

Computer noise

First to make things clear: The Synvoiz has an excellent signal-to-noise ratio. I don’t have calibrated measurement utilities but can tell you that the unit is silent when it needs to be. Compared to other analog or digital synthesizers it’s in the same ballpark.

Not so my lovely Retroverb. It’s a spring reverb and open to a lot of influences beside the input signal. Additionally it has a muffled sound so you tend to grab an equalizer and push those higher frequencies. Doing this last week I heard a noise which I know to good from bad wiring in cheap recording setups. Today’s CPUs change their power needs thousand times a second dependent on the load it is given. Even with modern plugins you won’t stress out your CPU to the max so it has idle times where it tries to save power (and heat emission). So it is likely that this emits to your audio cabling in some way. Here is an example of the Retroverb’s noisefloor with the interfering noise of the CPU:

It’s easy to exclude other sources by giving the CPU something heavy to do like the Prime95 tool. With the software running the noise floor of the unit sounds like this:

Please mind that the sound examples are heavily equalized so it’s clear what I am talking about.

The troubleshooting started. Replacing the audio cables didn’t help. Also I realized that it’s not input dependent which means the interfering noise comes from within the unit. Changing position of the PSU also didn’t get me any further but moving the whole unit removed the unpleasant sound. After switching off unit by unit nearby the Retroverb I found the culprit: The power supply cord of the TFT! At the beginning of my investigation I thought about the PSU of the computer or that of the Retroverb itself – which isn’t a standard DC one so not so easy to replace (12 v AC). After superseding the old cord with a new one the noise floor isn’t as polluted as before but you still hear it:

With a proper gain staging the noise is on a level I can live with for the moment as there is no better place for the Retroverb in my small room.

By the way when I activate the filter of the unit the signal-to-noise ratio is immediately reduced and the computer noise only barely noticeable. Filters tend to emit noise that’s the reason why in every synthesizer the filter comes before the VCA.


First contact

Finally! With a lot of excitement I unpack the wonderful produced wooden case.

Notice the plug for the power supply: a mini XLR!