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Noisy Audio In in sub 37, is normal?

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Noisy Audio In in sub 37, is normal?

Postby moogforum2 » Wed Nov 23, 2016 6:24 pm

Hi folks, i recently bought a Sub 37, and is a superb machine, but nevertheless there is something that I noticed a days ago when I was trying to use the Sub 37 Audio in with all oscillators, sub and noise off, well the manual clearly says: "You must press a key to pass external audio through the Sub 37. You also can use a Moog FS-1 footswitch, or simply press the LATCH ON button in the Ampli er Envelope section and make sure that the Ampli er Envelope’s SUSTAIN level is up.", but i have noticed that when a key is pressed or the Amp Latch is on there is a very quiet but noticeable sound although all Osc, sub oscillators and noise are off, basically my question is: Is normal to hear a very quiet noise when using only the fdbk/ext in and a key is pressed or the latch is on?
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Re: Noisy Audio In in sub 37, is normal?

Postby _DemonDan_ » Tue Dec 13, 2016 11:19 am

moogforum2 wrote:I have noticed that when a key is pressed or the Amp Latch is on there is a very quiet but noticeable sound although all Osc, sub oscillators and noise are off, basically my question is: Is normal to hear a very quiet noise when using only the fdbk/ext in and a key is pressed or the latch is on?

Hi moogforum2,

This is one of those situations where adding a cool feature also invites the risk of mild complaints.

As an example, on a ROM-based, sample-playback synth, very high Pitch Bend Depths (like 2 Octaves Up/Down) is a cool feature. But it allows people to push the samples up into a range where they might alias.

So... what do you do? Do you limit Pitch Bend Range to +/- 12 Steps so that the aliasing doesn't happen? Or do you allow the musically useful option of a wider Pitch Bend Range and sometimes risk getting aliasing complaints? (Me, I want options, even if they're not always perfect.)

Now... back to analog synths. A typical non-modular analog synth always has very loud, never-ending Oscillators going into a Filter which then goes to an Amplifier that is typically fully off when there are no notes being sounded.

In other words, whenever the synth is not making sound, it's only because the very last part of the audio chain is fully attenuated. But those oscillators are still going strong.

But... if you're using Audio In, all by itself, with other (normally on) sound sources shut off, and then fully open the final floodgates (LATCH ON or SUSTAIN = 100% with a key pressed) while not actually sending full-volume audio into the Audio In... you're going to hear some background noise.

To use a guitar analogy, if you have multiple gains between your guitar and amp, you're going to hear some noise when you're not actually playing any notes. The moment you are playing notes, the difference in volume between playing a string and not playing a string is so great that you can no longer hear the background noise (until the string fades away and the background noise comes up again).

The short version is this: Once you're putting sufficiently strong audio signals into the Sub 37's AUDIO IN jack such that you don't have to crank the FEEDBACK/AUDIO IN knob (which, on purpose, adds distortion after 12 o'clock), you won't have any problems with background noise.

And if you really want the synth (using Audio In) to get silent, then avoid locking the AMP fully open (via LATCH ON) and set the AMP ENVELOPE parameters to go silent (either instantly or over time) after releasing a key. Now you're once again allowing the AMP to do one of its main jobs: keeping the entire synth silent when it's supposed to.

Hope this helps.
_ :twisted: _DemonDan_ :twisted: _
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Re: Noisy Audio In in sub 37, is normal?

Postby moogforum2 » Wed Dec 14, 2016 2:54 pm

Thank you very much, your answer was clear but explicative, you are right I have noticed this "latch" sound on several synths with Audio In, so we can say is "Normal", I think that being careful with values and proper Amp EG configuration can also help a lot, thanks again!!!
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Re: Noisy Audio In in sub 37, is normal?

Postby ziggomatic » Sat Dec 31, 2016 1:31 am

hi,

is it normal that even all the mixer sound sources are off with the filter closed there's noise coming out when a press a key?

thanks :)
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Re: Noisy Audio In in sub 37, is normal?

Postby moogforum2 » Thu Jan 12, 2017 9:59 pm

Well i think it is the sound of the amp envelope and is normal in analog synths , but in the case of the Sub 37 is a just little noisy, hope it can be a fixed a little in a next firmware, like Moog do with some offending frequencies of the oscillators.
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