residual noise on midibox sid

[matcom]

Hi:

in my first midibox sid i notice that when u release any note u can hear this note continously at low volume.

i want to know if this is normal or theres any solution for it. ive tryed with 4 diferent SIDs that i have with the same results. Btw i have 4 SIDS 3 of them are made in korea and the other its made in thailand..well, the Thailand one sound more.... how to tell...more "crunchy" ... maybe its my imagination.

other curious thing its the "hum" of the system its alocated at 100hz, 200hz, 300hz and 400hz exactly... but i think this depends of the power suply u use.

Thx

[TK.]

Hi,

you are using 6581s, right?

There is no real help, it's the VCA leackge issue, which cannot mute the oscillators completely.

And yes, there are also variations between the SIDs, see

http://www.midibox.org/forum/index.php?topic=9135.msg66996#msg66996

Best Regards, Thorsten.

[jrp]

Isn´t it possible to output a cv for a filter or vca? (with aout module)

or was that the fm?

If that is possible, and i bet it is, this could be a solution.

Make a vca follow the envelope of the sid´s soundpatch.

Or use a simple noisegate. If you like the sound to be dirty you can try the following:

A amp stage with variable gain, followed by two antiparallel diodes. Set the gain so that the softest part of the sound is just passing the diodes. Everything below +- 0,3v will be cut away. So you have to boost quite a bit. This is a great methode for distortion boxes, don´t know if you like the sound with the sid.

A real noisgate is more complex, but still a simple build.

basically a envelope follower to detect the amplitude, a comparator and a vca. if you can´t find a shematic i can have a look. (but i would have to look, that´s why i don´t post it now...)

[TK.]

We had this suggestion many times, but my assumption is: when somebody asks such generic questions, it will be very difficult for him to build and setup external DACs and VCAs

Such an option will only be supported by MBSID V2 anyhow (see the appr. postings about external outputs)

But to make it short: it's still a tinkering solution - it especially won't work on multi or drum patches

Better solution: use a 8580 or 6582, or some Fx VSTs like an envelope follower or noisegate (like you mentioned)

Best Regards, Thorsten.

[jrp]

yes, of course, i hadn´t thought of that. Using different voices at one time this won´t work. Still i think the possibility to output the egs as cv is a very powerful feature! :D FM or Sid with minimoogfilter and tube vca 8)

Ok, a noisegate would be best. In a studio setup this would be the obvious solution. Wonder why this problem is not present when running the chip in a c64 though.

About the simple diode noisegate, i forgot to mention that low drop fast diodes should be used. BAT 43 work fine.

[jrp]

and my oppinion is that building an aout and a vca is no difficult task. Not much harder than soldering a core or any other module.

It´s just like with all electronics: for easy troubleshooting you need to go step by step. Buld the sid, see if it works. Build the vca, can be a simple one, apply a voltage that should make it open, see if you hear something. Build the Aout (LC would be fine) and see if it outputs a cv. Connect everything and trim so that the vca is shut when no key is pressed. Ok, these are many more things to watch out for than building a simple setup, but if you go one by one nothing should go wrong.

[stryd_one]

other curious thing its the "hum" of the system its alocated at 100hz, 200hz, 300hz and 400hz exactly... but i think this depends of the power suply u use.

That *could* be a ground hum from 50Hz AC power... Are you using the optimized PSU?

[jrp]

i´m sure it is from the psu. multiples of 50hz - sounds a lot like a bad filtered psu.

[TK.]

Wonder why this problem is not present when running the chip in a c64 though.

the same issue exists when the SID is controlled from a C64 of course.

It also exists on other SID synths, like the SIDstation, and people have learned to live with this...

Have you ever heard the background noise we are talking about? ;)

I mean - the s/n ratio is about -60 dB on a 6581, and ca. -90 dB on a 8580 (depending on the quality of the PSU), therefore you only notice it when the SID is silent (which was not the case in C64 tunes ;)), and when the audio output is dynamically amplified, e.g. with a compressor.

But there are simple Fx (e.g. VST) based solutions without need for additional hardware to remove the background noise completely if desired. Also - if a compressor is used, tweak on the parameters (keyword: knee) so that at a certain silence level the output won't be amplified.

I for myself mostly don't use such measures, there is just no real need for this -> in the mix <-

Therefore I don't understand the endless discussions about alternative, more complex and more expensive solutions. I also don't know, who should document and support all these solutions...

However, if this is a 50 Hz buzz, then it is another problem of course.

Have you grounded the unused audio in channel? (strongly suggested)

Best Regards, Thorsten.

[doc]

But there are simple Fx (e.g. VST) based solutions without need for additional hardware to remove the background noise completely if desired. Also - if a compressor is used, tweak on the parameters (keyword: knee) so that at a certain silence level the output won't be amplified.

... or just take a (VST-) noisegate (that's what I use). I also think the noise isn't a issue to discuss again and again. Just "custumize" the output a little (compressor/limiter) and you'll see it works!

greets

Doc