Noise novation circuit?

[Funkaroma]

Hi guys,

I wonder how I could fix this. When I’m plugging my headphones directly into the unit I have zero noise, but when I’m recording something through my audio interface there is this fairly high constant rate of noise. I thought it where the cables, but when I plugged the same cables into my monologue there wasn’t any noise. Also the out coming gain is very low compared to the monologue. I’m using a presonus audiobox to record the music. I feel like the overall quality besides the noise is also lower then when I am plugging just my headphones in.

[JCJR]

Is the noise hum, hiss, digital whine or digital hash kind of sound? The digital hash might kinda sound like low level what old phone line modems sounded like. Or a combination of noise types?

Do you power the device with USB or the 12 volt dc connection (a wallwart transformer)?

Sometimes noise in addition to hums can happen from various ground loops. Maybe the only way to know would be to try and cure possible ground loops and maybe the problem goes away and maybe (if it is not a grounding issue) the noise remains.

Maybe there would be a smarter way to diagnose the cause, but process of elimination is not a bad way to solve a bug.

I will guess that you might eliminate some ground loop possibilities by test running the device standalone (no USB midi or din midi connection to computer). Power the device with a good quality 12 volt wallwart transformer.

Finally make the audio connection between device and computer audio interface with a "hum eliminator" type isolation transformer. The least expensive one which some folks say works pretty good is a little stereo hum isolation transformer box by behringer. Very affordable.

It might seem a shame even spending a few bucks on an isolation transformer that MAY or MAY NOT fix your problem, but even if it doesn't fix this problem then an isolation transformer is handy to have around in case it is needed, even if you don't need it right this minute.

If running standalone like that fixes the noise then possibly you could get new noise when you hook up USB or din midi to the computer establishing another possible route for ground loops or digital hash leakage.

That is the "method of elimination" to locate if there is one problem or multiple problems.

It is always possible you have no ground loop issues at all but your novation's line output circuitry is not working right.

So maybe a first elimination test before fooling with isolation transformer and interface: Run the synth standalone powered with a good quality 12 volt wallwart and plug the outputs into a good quality keyboard amp or PA system or some kind of sound system that you know sounds good with instruments.

If it sounds like krap plugged into a good PA then MAYBE an isolation transformer would help but this result would be fairly strong indication that the novation line output circuit is somewhat fried and needs fixing.

[Funkaroma]

Is the noise hum, hiss, digital whine or digital hash kind of sound? The digital hash might kinda sound like low level what old phone line modems sounded like. Or a combination of noise types?

Do you power the device with USB or the 12 volt dc connection (a wallwart transformer)?

Sometimes noise in addition to hums can happen from various ground loops. Maybe the only way to know would be to try and cure possible ground loops and maybe the problem goes away and maybe (if it is not a grounding issue) the noise remains.

Maybe there would be a smarter way to diagnose the cause, but process of elimination is not a bad way to solve a bug.

I will guess that you might eliminate some ground loop possibilities by test running the device standalone (no USB midi or din midi connection to computer). Power the device with a good quality 12 volt wallwart transformer.

Finally make the audio connection between device and computer audio interface with a "hum eliminator" type isolation transformer. The least expensive one which some folks say works pretty good is a little stereo hum isolation transformer box by behringer. Very affordable.

It might seem a shame even spending a few bucks on an isolation transformer that MAY or MAY NOT fix your problem, but even if it doesn't fix this problem then an isolation transformer is handy to have around in case it is needed, even if you don't need it right this minute.

If running standalone like that fixes the noise then possibly you could get new noise when you hook up USB or din midi to the computer establishing another possible route for ground loops or digital hash leakage.

That is the "method of elimination" to locate if there is one problem or multiple problems.

It is always possible you have no ground loop issues at all but your novation's line output circuitry is not working right.

So maybe a first elimination test before fooling with isolation transformer and interface: Run the synth standalone powered with a good quality 12 volt wallwart and plug the outputs into a good quality keyboard amp or PA system or some kind of sound system that you know sounds good with instruments.

If it sounds like krap plugged into a good PA then MAYBE an isolation transformer would help but this result would be fairly strong indication that the novation line output circuit is somewhat fried and needs fixing.

I don’t how I can explain what kind of noise it is. I made a small demo of the noise. 1st part is when I put the gain around 40% and the other one like 60% on my audio interface. The gain knob on the circuit itself doesn’t affect the amount of noise.

https://soundcloud.com/coentromer/noise-test/s-WFxLW

I power it with the wall adapter where the unit came with. I don’t have any batteries in circuit.

I don’t have a huge amount of stuff to test what would work like ground loop filters etc. Buying stuff which may or may not work is not the ideal situation indeed. I’ve bought the circuit second hand, but there is still warranty on it. It would be a shame if it was broken though. I wonder how it can be that the outcoming signal of the circuit is so much lower then the monologue. When I sync them up and balance the volume and the circuit is all the way to 100 the monologue is not even at 20.

[thecontrolcentre]

Are you setting the gains on your interface correctly? The circuit may need more than the monologue. I would also try running Circuit on batteries only, to see if that fixes the noise issue.

[JCJR]

So far as my old ears can detect, the noise sounds like a mild buzz plus a little broadband hiss. Buzz is the "higher harmonics" of power line sine wave AC frequency, often 60 or 50 Hz depending on where you live. Its like if you clip a sine wave into a squarish wave and then do various filterings to pick out various higher harmonic groupings of the multiples of 60 Hz. You could have low-mid frequency buzz, midrange buzz, high-frequency-only buzz, whatever, just depending on accidents of circuitry. The "hum" is just the purer low first few harmonics of the power line frequency, mostly heard in the woofers not the mids or tweeters of your speaker. Hum could have maybe 1st, 2nd, and 3rd harmonic mix and still sound fairly pure and bassy (for 60 Hz power, a mix of 60 Hz, 120 Hz, 180 Hz).

Can come from lots of sources including neon sign transformers, household lighting dimmers, some of the "noisier circuit" flourescent, compact flourescent, and LED household lights. And some kinds of circuits just naturally seem to make the buzz, guitar amps and such, even in absence of specific interference sources. Maybe some switching power supplies can help make that kind of noise too. Switching power supplies are the most common kind nowadays because they are so much more energy efficient than old analog regulated supplies.

Maybe an isolation transformer wouldn't help or maybe it would help but that Behringer Hum Destroyer is only about 24 bux US$. https://www.sweetwater.com/store/detail ... -destroyer

That is a good idea trying it on batteries to see if it helps. Possibly some of the problem could be coming in from the wallwart transformer.

If you have a stereo 1/8 inch plug to dual quarter inch plugs adapter, or some combination of adapters that would get you there, you could see if MAYBE the sound would be hotter or cleaner recording from the headphone output. I mean, if the headphone output sounds better then why not use it? But if it is some kind of ground loop and the buzz happens when you connect to the audio interface, then the ground loop would happen regardless which outputs on the synth you use. Its just something to try.

That synth might jus be designed to have a quieter output. Without data its just guesswork. Maybe somewhere the manufacturer states what the output level is supposed to be in the specs or manual?

This wikipedia article explains about line level standards: https://en.wikipedia.org/wiki/Line_level

Common are +4 and -10 as explained in the article. It might be that one of your synths was designed to be +4 and the other was designed to be -10. I personally think it would be silly for anyone to sell synths nowadays unless at least capable of +4 but it is only my opinion.

[Funkaroma]

Hi,

So I’ve tried a couple things, but I’m almost completely sure that the problem has to do something with my audio interface. On my old pc I had this problem that it couldn’t reconize it properly. Sometimes it did, but most of the time it didn’t and a gave me big headaches. I decided to instal ableton on my newer pc and a few days everything worked fine until the problem appeared all of a sudden also on this pc.

I connected to circuit directly to my speakers and I had no noise issue at all and the outcoming gain was way louder then what I could get from the audio interface. The weird thing is that my monologue doesn’t have this problem? I use the dedicated drivers for the audiobox. Could it be that asio4all could fix my problem? I don’t know a lot of it, but I don’t know.. It would be kinda odd if that would fix the problem with the gain etc.

[JCJR]

Sorry you are having problems. It is a puzzle. Anything is possible. Maybe it is somehow the fault of the audio interface. Or not. Hard to guess. Do you know anyone with other interfaces you could test with? Eliminate or confirm the suspicion?

A few low-probability ideas--

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Is the audio interface input unbalanced tip-sleeve, or balanced ring-tip-sleeve? Similarly, do you know if your synths are balanced or unbalanced?

The modern balanced models are generally always tranformerless. A balanced sender, the output, sends the exact same signal out both the tip and the ring (with the sleeve the common ground return). The only difference is that the two signals are 180 degrees inverted. So if you connect with a ring-tip-sleeve plug to a balanced input, the voltage that the input sees is double. For instance if the signal at one point peaks at +1 volts on the tip, then the signal will simultaneously peak at -1 volt on the ring. So the balanced input will see a 2 volt peak, the difference between +1 and -1 volts. Also the balanced input will tend to cancel out some kinds of noise on the cable connection, called Common Mode Noise Rejection. Just like +1 - (-1) = 2, if the same noise happens to be on both tip and ring, then [noise - the same noise] = no noise. Less noise and a +6 dB hotter signal. Win-Win.

Those balanced outputs and inputs are also compatible with unbalanced tip-sleeve. If you plug an unbalanced tip-sleeve plug into a balanced output it just shorts and ignores the ring output, and passes on the tip output only. Those kind of circuits are (hopefully) designed so they are sposed to work into that kind of short "forever" without causing damage to the driver. So the only two disadvantages is that there is less noise rejection and the output signal is -6 dB quieter than the balanced connection. The tip-sleeve cable plugged into the balanced input jack gets signal on tip and nothing on ring. So it does the subtraction +1 - 0 = +1, half the level you would have got with a balanced connection.

Just sayin, if both your interface and synth can do ring-tip-sleeve balanced, it ought to be hotter (and maybe a little less noise) connected using ring-tip-sleeve cables.

NOW MAYBE, depending on how individual jacks on the gear are constructed, if your interface is balanced but your synth output is unbalanced, then you should make sure to use unbalanced tip-sleeve cables? In some cases if you connect an unbalanced synth to a balanced input using a ring-tip-sleeve cable, the ring connection would end up "floating" on the synth end, rather than grounded, so could be a source of unwanted noise injection at the input jack.

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Another low-probability thang. Possibly related to the above balanced/unbalanced issue but doesn't have to be. If your interface input impedance is lower than the synth wants to drive, then you will lose volume and possibly when pushed start getting a little distortion. In modern time this is extremely unlikely. But electronically possible.

Nowadays line outputs virtually always have an output impedance lower than 1000 ohms. In fact a lot of the nicer line level gear has output impedance around 50 or 100 ohms. That means they will deliver their full rated output level into that low of an impedance without distortion or circuit damage. However if you did run a 100 ohm output impedance into a 100 ohm input impedance, then the two impedances would act like a voltage divider. Half of the voltage would dissipate inside the sender and half would dissipate inside the receiver, so you would cut the output in half, about a -6 dB loss.

So usually we want the receiver line input impedance to be quite a bit bigger than the sender output impedance, so most of the voltage is dissipated inside the receiver and we don't have significant loss.

A lot of line inputs nowadays seem to have input impedance around 10000 ohms or higher, so that there is virtually no "voltage divider loss" driving a 10000 ohm input from a 100 ohm output. The loss is only 100/10100 = 0.0099 or about 1 percent or about -0.086 dB.

But you could have some "voltage divider" impedance losses if the source and destination impedances are too similar. A good rule of thumb is to have the destination impedance at least 10X as big as the source impedance, but closer impedances will work, you just get some losses if they are too close to each other.

So you could check what the source impedance of your synths and input impedance of your interface is sposed to be. As said, unlikely a problem nowadays but possible.

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Here is an even lower-probability thang-- I have seen cases where some old synthesizers had "not good enough" output antialiasing filters, and though they sounded fine to the ear connected to speakers, and they sounded good recorded on good audio interfaces with excellent input antialiasing filters, they would sound very distorted/nasty recorded into an audio interface with not very good input antialiasing filters.

I don't know if the same phenomena could increase noise. Maybe. Dunno.

The thing was, the inexpensive audio interfaces generally sounded fine recording from microphones or good-quality synthesizers. The inexpensive interface worked great for the money recording properly band-limited audio. They only sounded nasty when recording synthesizers with inadequate output filtering. And the ear can't always tell which synth has good or bad output antialias filtering because that crap tends to be above the range of human hearing.

So it was just one of those strange thangs, certain synths needed to be recorded on high quality interfaces that had good enough input filters to keep that high-frequency inaudible hash out of the signal.

I would have guessed that problem would be long in the past and nowadays just about any audio interface has "good enough" input antialiasing filters, but dunno one way or the other.