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DIY Stompboxes => Digital & DSP => Topic started by: AndyF on July 14, 2021, 11:40:33 AM

Title: FV SPIN - NOISE
Post by: AndyF on July 14, 2021, 11:40:33 AM
Hello, I tell you I have tried different schemes, more than 50 algorithms, my own and others that I got out there.
The conclusion is that there is noise in all of them, in some more, depending on the type of effect, you can hear a lot.
The solution to filter the output of the fv spin, the problem is that I cannot find a balance between what is filtered and the sound is darkened, with the elimination of the blowing of the fv spin itself.

So, has someone made something interesting that they can share with a schematic, or some tips to solve this?

Ldo regulators do not influence anything.
The pcb design is, but it is not decisive.
Different types of mixes make the fv spin noise more or less heard, but when you want to achieve wet / dry the noise is a lot. There are brands on the market that launch their products with tremendous noise, I can't explain how they don't care.

ok, if some genius can give a solution I will appreciate it for all eternity :-)

thanks
Title: Re: FV SPIN - NOISE
Post by: vigilante397 on July 14, 2021, 11:45:21 AM
Welcome to the forum :)

What have you tried? It's hard to know what to tell you without knowing where you're starting from. The FV-1 isn't a hi-fi chip so you can't expect noiseless, but plenty of people have gotten great results with it. At the end of the day you have to know how much noise you're willing to accept though, hopefully you aren't expecting crystal clear hi-fi sound.
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 14, 2021, 12:15:15 PM
Welcome to the forum :)

What have you tried? It's hard to know what to tell you without knowing where you're starting from. The FV-1 isn't a hi-fi chip so you can't expect noiseless, but plenty of people have gotten great results with it. At the end of the day you have to know how much noise you're willing to accept though, hopefully you aren't expecting crystal clear hi-fi sound.

Exactly, the noise is always there, I can't explain why the manufacturer doesn't solve it. This circuit is the one that I like the most but the one that gets a lot of noise and I can't find how to modify it.
(https://i.postimg.cc/vxfLzf2n/SCHEMATIC-FV-SPIN.jpg) (https://postimg.cc/vxfLzf2n)
Title: Re: FV SPIN - NOISE
Post by: ElectricDruid on July 14, 2021, 12:26:45 PM
Welcome!

I can't explain why the manufacturer doesn't solve it.

Probably because designing noiseless ADCs and DACs on the same silicon as a processor is *extremely* difficult. It's one of the reasons codec chips are always separate from DSPs (otherwise it would be very handy to have the ADC/DAC on the same chip, but apart from the FV-1 hardly anyone does).

Quote
This circuit is the one that I like the most but the one that gets a lot of noise and I can't find how to modify it.
(https://i.postimg.cc/vxfLzf2n/SCHEMATIC-FV-SPIN.jpg) (https://postimg.cc/vxfLzf2n)
You could get all "old school" with it and add a 571 compander circuit like a BBD delay. That would give you a better signal level going in and squash the noise coming out.

One other trick I've seen suggested is to feed a differential input signal to the FV-1's inputs, and then combine the two outputs at the other end. That should cancel any common mode noise, at least. How much improvement that makes, I can't say - I haven't tried it myself.

HTH
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 14, 2021, 02:45:00 PM
Welcome!

I can't explain why the manufacturer doesn't solve it.

Probably because designing noiseless ADCs and DACs on the same silicon as a processor is *extremely* difficult. It's one of the reasons codec chips are always separate from DSPs (otherwise it would be very handy to have the ADC/DAC on the same chip, but apart from the FV-1 hardly anyone does).

Quote
This circuit is the one that I like the most but the one that gets a lot of noise and I can't find how to modify it.
(https://i.postimg.cc/vxfLzf2n/SCHEMATIC-FV-SPIN.jpg) (https://postimg.cc/vxfLzf2n)
You could get all "old school" with it and add a 571 compander circuit like a BBD delay. That would give you a better signal level going in and squash the noise coming out.

One other trick I've seen suggested is to feed a differential input signal to the FV-1's inputs, and then combine the two outputs at the other end. That should cancel any common mode noise, at least. How much improvement that makes, I can't say - I haven't tried it myself.

HTH

ok thanks, among so many things tried, you should try this.
Hopefully someone else contributes other ideas.

Now it would be much easier if the manufacturer indicated how to solve this, when you write in their forum, they only describe what is the design, the regulator, the algorithm, the problem is never the fv spin ...
that is wrong! The fv spin is the noise generator, which of course, depending on what you input, will come out better or worse, but always with noise.
Title: Re: FV SPIN - NOISE
Post by: vigilante397 on July 14, 2021, 02:51:49 PM
The fv spin is the noise generator, which of course, depending on what you input, will come out better or worse, but always with noise.

I was afraid you would say that :P Have you looked into the FX-Core from Experimental Noize? Similar-ish to FV-1 but more powerful and uses external CODECs like Tom mentioned, so it would be much more suited for a low noise solution. It sounds like you're expecting a lot from an inexpensive all-in-one package that was designed more to be user-friendly than to be perfect.
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 14, 2021, 04:56:09 PM
The fv spin is the noise generator, which of course, depending on what you input, will come out better or worse, but always with noise.

I was afraid you would say that :P Have you looked into the FX-Core from Experimental Noize? Similar-ish to FV-1 but more powerful and uses external CODECs like Tom mentioned, so it would be much more suited for a low noise solution. It sounds like you're expecting a lot from an inexpensive all-in-one package that was designed more to be user-friendly than to be perfect.


I understand what you say, what I do not share that things are done more or less, for me they are good or bad, and I believe that something can be achieved well, but I don't know how to do it.
The fx core, I saw it but for now I am not interested in getting involved with it, I do not see it so simple.
thanks for your answers ...
Title: Re: FV SPIN - NOISE
Post by: MetalGuy on July 14, 2021, 05:56:01 PM
Never noticed FV-1 was noisy. Ears are still good though.
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 14, 2021, 06:00:11 PM
Never noticed FV-1 was noisy. Ears are still good though.

with respect friend, you should try to listen better, in all the circuits that contain the fv spin there is noise, unfortunately.
because it is very good to do effects.

But hey maybe you have a schematic designed that overrides this, and it would be great if you help me.
Title: Re: FV SPIN - NOISE
Post by: ElectricDruid on July 14, 2021, 07:12:15 PM
I think there might be a degree of "expectation management" required here. :icon_lol:

If you buy a simple chip for not a lot of money, it is highly unlikely to do the same job as a more sophisticated and expensive group of chips that (on paper) do a similar thing. You can do a basic delay using an FV-1. You can do it using a STM32-F4 with bags of RAM and a serious codec attached. One gives a better technical result than the other. Examples of 570/571 companders are all over the internet (

Which do you want to do? How much money and development time are you willing to spend?

Those questions affect the quality you can expect to get.

Sure, you can do stuff to improve the FV-1, but if it's not in the ballpark that you want to play in, you need to adjust you ideas (and prices!) accordingly.


Title: Re: FV SPIN - NOISE
Post by: potul on July 15, 2021, 03:49:37 AM

One other trick I've seen suggested is to feed a differential input signal to the FV-1's inputs, and then combine the two outputs at the other end. That should cancel any common mode noise, at least. How much improvement that makes, I can't say - I haven't tried it myself.


Interesting one. Will this require to code the program in stereo, so that both signals are processed equally before merging them?
Title: Re: FV SPIN - NOISE
Post by: free electron on July 15, 2021, 09:21:19 AM
I think you can just read the adcr adcl and use the difference as the input signal, processed further as mono.
At the end, do the opposite: write sig_out to dacl, sig_out*-1.0 to dacr and use differential amp + some lowpass filtering.
The key would be to cancel out the internal ADC+DAC noise.
The question is, tough: does the ADC sample the L and R signal exactly at the same time?
Also nothing forbids using separate 3.3V regulators for the analog and digital part.
Title: Re: FV SPIN - NOISE
Post by: ElectricDruid on July 15, 2021, 09:27:43 AM

One other trick I've seen suggested is to feed a differential input signal to the FV-1's inputs, and then combine the two outputs at the other end. That should cancel any common mode noise, at least. How much improvement that makes, I can't say - I haven't tried it myself.


Interesting one. Will this require to code the program in stereo, so that both signals are processed equally before merging them?

As free electron says, you could invert one of the inputs and merge internally. That should cancel common mode noise in the ADC. Then you could process in mono, and then flip one channel again before sending to the DAC. Then the analog side uses a differential amp to regain the signal and cancel any DAC noise.

Or as you say, you could process the two entire chains identically. That might even start to cancel stuff like rounding errors in the algorithm, if they're consistent. Dunno.


Has anyone actually done a proper test on the chip? If you feed a string of zero values to the DAC, how much noise does it produce?
If you ground the inputs and read the ADC value, how much noise is there on the readings? I've never tried, but it never seemed noisy to me.

Title: Re: FV SPIN - NOISE
Post by: octfrank on July 15, 2021, 11:06:29 AM
If you ground the inputs and read the ADC value, how much noise is there on the readings? I've never tried, but it never seemed noisy to me.

Actually you want to run a Vcc/2 signal in as the converters are signed so ground is actually -1.0.

Also keep in mind these are delta-sigma which means they do not really like DC so best to use something like a 1KHz signal at -6db.

Most noise issues are related to PCB layout (poor ground plane, bad routing, etc.), power supply noise (if it goes away on battery then it is the power supply) or a low input signal so they are adding lots of gain then complaining that there is noise (run a hotter signal in).
Title: Re: FV SPIN - NOISE
Post by: ElectricDruid on July 15, 2021, 11:37:18 AM
Actually you want to run a Vcc/2 signal in as the converters are signed so ground is actually -1.0.
Doh, yeah, 'course. 3V3 single supply. Silly me.

Quote
Also keep in mind these are delta-sigma which means they do not really like DC so best to use something like a 1KHz signal at -6db.
Ah, ok. So time for a sine wave test signal then!

Quote
Most noise issues are related to PCB layout (poor ground plane, bad routing, etc.), power supply noise (if it goes away on battery then it is the power supply) or a low input signal so they are adding lots of gain then complaining that there is noise (run a hotter signal in).
Clearly for best quality, you need a decent level going in. 3.3V isn't a lot of headroom, so it all counts. That was why I suggested a compander - and for the retro-cool factor too, of course ;) Some regulators are a lot quieter than others, so I imagine that makes a difference too. Do you know how important it is to use separate analog and digital supplies, Frank? A lot of circuits I've seen don't, but I'm guessing it makes a noticeable difference or you wouldn't have bothered including the option.
Title: Re: FV SPIN - NOISE
Post by: octfrank on July 15, 2021, 12:09:27 PM
Clearly for best quality, you need a decent level going in. 3.3V isn't a lot of headroom, so it all counts. That was why I suggested a compander - and for the retro-cool factor too, of course ;) Some regulators are a lot quieter than others, so I imagine that makes a difference too. Do you know how important it is to use separate analog and digital supplies, Frank? A lot of circuits I've seen don't, but I'm guessing it makes a noticeable difference or you wouldn't have bothered including the option.

All your comments above have been great, especially the one about "expectation management", every design from chips to pedals is all about that.

As to split supplies, it really depends on the product. For most pedals there will be little to no advantage, most pedals are simply designed to have just the FV-1 as the only digital component (oh, and the 24LC32A) so good bypassing right at the pins is all that is needed. But if it is a more complex device with a micro doing USB and MIDI, a display, etc. then yes, get all that digital noise off the analog supply. In this case you may choose to run the FV-1 as split supplies or completely off the analog supply. In fact the only time we run split supplies on the chip is in test as there are a ton of digital components on the tester so having an isolated analog supply is necessary to make clean measurements of the converters.
Title: Re: FV SPIN - NOISE
Post by: Sweetalk on July 16, 2021, 05:43:44 AM
Welcome to the forum :)

What have you tried? It's hard to know what to tell you without knowing where you're starting from. The FV-1 isn't a hi-fi chip so you can't expect noiseless, but plenty of people have gotten great results with it. At the end of the day you have to know how much noise you're willing to accept though, hopefully you aren't expecting crystal clear hi-fi sound.

Exactly, the noise is always there, I can't explain why the manufacturer doesn't solve it. This circuit is the one that I like the most but the one that gets a lot of noise and I can't find how to modify it.
(https://i.postimg.cc/vxfLzf2n/SCHEMATIC-FV-SPIN.jpg) (https://postimg.cc/vxfLzf2n)

One of the issues with this circuit is that the input signal is low in amplitude. For better signal to noise ratio you want the input to be as hot as possible without clipping, so you need another to amplify the signal before hitting the FV1. You want to have it as close as possible to 3vpp.

Another thing is that diodes clampling the ADC to 3v3/2, is not necessary because the ADCs are internally biased to Vcc/2. Don't know if this adds noise, but never used in my designs. At least you gain in lower the parts count.

Layout REALLY matters, I have some boards with the FV1 that has poor layout and compared with others that haves a proper layout the difference is HUGE. Ground every pin with it's own via to a ground plane and add decoupling caps to every voltage pin, 0,1uF will do the trick.

Also, in that circuit you don't have any output HPF-LPF to get rid of the out of band noise. That is a must!. I always use a 2nd order LPF on the output.

Title: Re: FV SPIN - NOISE
Post by: MetalGuy on July 16, 2021, 04:33:23 PM
There's an FV-1 forum project thread which is a good starting point for an FV-1 project (pedal).
Title: Re: FV SPIN - NOISE
Post by: pruttelherrie on July 17, 2021, 04:38:22 AM
Excuse my ignorance, please educate me if I'm wrong:
(https://i.postimg.cc/vxfLzf2n/SCHEMATIC-FV-SPIN.jpg) (https://postimg.cc/vxfLzf2n)

One of the issues with this circuit is that the input signal is low in amplitude. For better signal to noise ratio you want the input to be as hot as possible without clipping, so you need another to amplify the signal before hitting the FV1. You want to have it as close as possible to 3vpp.
Fair enough, the input buffer could/should be made 'boostable'.

Quote
Another thing is that diodes clampling the ADC to 3v3/2, is not necessary because the ADCs are internally biased to Vcc/2. Don't know if this adds noise, but never used in my designs. At least you gain in lower the parts count.
As I understand it, these diodes are there for protection? What's the difference between protecting and clamping? (Note that they are Schottky's, not zeners. I don't agree on the symbol used though.)

Quote
Layout REALLY matters, I have some boards with the FV1 that has poor layout and compared with others that haves a proper layout the difference is HUGE. Ground every pin with it's own via to a ground plane and add decoupling caps to every voltage pin, 0,1uF will do the trick.
Agree 100%!

Quote
Also, in that circuit you don't have any output HPF-LPF to get rid of the out of band noise. That is a must!. I always use a 2nd order LPF on the output.
Strictly speaking, the cap on the output buffer is a 1st order LPF? Corner frequency of 1 / (2 * pi * 0.00000068 * 15000) = 15 Hz?!?!? Huh?
Title: Re: FV SPIN - NOISE
Post by: Sweetalk on July 17, 2021, 05:23:06 AM
As I understand it, these diodes are there for protection? What's the difference between protecting and clamping? (Note that they are Schottky's, not zeners. I don't agree on the symbol used though.)
Yeah, Schottky's!, my bad

Quote
Also, in that circuit you don't have any output HPF-LPF to get rid of the out of band noise. That is a must!. I always use a 2nd order LPF on the output.
Strictly speaking, the cap on the output buffer is a 1st order LPF? Corner frequency of 1 / (2 * pi * 0.00000068 * 15000) = 15 Hz?!?!? Huh?
[/quote]

Yes, that cap acts like a LPF but dependant of the gain of that stage. Also, when your signal reaches that stage you already mixed the "noisy" signal from the FV1 with the clean in the mix control. You want to do all the reconstruction filtering right after the DAC and then keep processing the signal, mixing, etc.
Title: Re: FV SPIN - NOISE
Post by: pruttelherrie on July 17, 2021, 06:37:09 AM
when your signal reaches that stage you already mixed the "noisy" signal from the FV1 with the clean in the mix control. You want to do all the reconstruction filtering right after the DAC and then keep processing the signal, mixing, etc.
Ah right! Thanks for the insight.
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 17, 2021, 06:38:02 PM
ok I read everything, now as I wrote at the beginning of the thread, the noise can be eliminated, but there is no concrete clarity on how to do it, they are all said assumptions, nobody published anything that says this has no noise, I guarantee it! And the one who has it, I don't know if he will share it clearly because it is a job and it is a challenge to do it. I tried many pedals that use the fv spin, and I can say in particular that there are important brands that release their product with a lot of noise in my opinion and others that have almost zero noise, none have zero noise! Therefore, it can always be improved, but the noise is there and it is not something easy to eliminate.
Of course, using a poor quality power supply will not help, they are things that are discarded. A good pcb design? And yes, I think it makes a difference, as well as the algorithms will ...
Now if all this is known and it is understood that it is not very easy to do something that does not produce and amplify the noises, because xnoize does not give parameters of things that should or should not be done, and things that should or should be done, You have to look a lot to be able to do something almost decent, without obtaining totally satisfactory results. I believe that many are satisfied with the result and accept it and relax, but the noise is there and it tortures me to have it there ...
For example, in a reverb or a delay, you hardly use the mix to the maximum, so the noise you will not notice, so you use it without problems until the day you decide to try new things and find a hurricane of background noise and it is impossible to record in a pc with tremendous noise. In a chorus, in a pahser, that all the mixing is needed it is a big problem to do something good without noise.

It must be me, I'm very bad at all this and all the rest must be great experts, but as you know, we all start one day, and my intention is not to criticize the product because for me a great solution is great, but I do not understand how everything This noise issue passes by and nobody says or does anything to improve it, as there is no basic list of use and solutions to possible problems, it would be less frustrating.
Of course when you sell a lot you don't need to do anything else, leave it like that, it totally works, right?

Thanks to all who have responded, I hope someone contributes something concrete and tested, I would pay what I do not have to eliminate the damn noise, my message box is open to receive all possible help ;D
Title: Re: FV SPIN - NOISE
Post by: ElectricDruid on July 18, 2021, 06:07:08 PM
You keep telling us how bad it is, but you haven't put any numbers on it. What is this "unacceptable" noise level you're seeing coming out of this chip? How many mV P-P on average? Or RMS, or whatever? I don't really care *what* measure you use as long as it's something we can relate to.

If we have a number on the noise that you've got, we might be able to get a figure on the S/N that you might hope for, and that might give us some idea whether you're being realistic or aiming for the moon in a flying bucket! ;)
Title: Re: FV SPIN - NOISE
Post by: Sweetalk on July 19, 2021, 05:45:08 AM
You keep telling us how bad it is, but you haven't put any numbers on it. What is this "unacceptable" noise level you're seeing coming out of this chip? How many mV P-P on average? Or RMS, or whatever? I don't really care *what* measure you use as long as it's something we can relate to.

If we have a number on the noise that you've got, we might be able to get a figure on the S/N that you might hope for, and that might give us some idea whether you're being realistic or aiming for the moon in a flying bucket! ;)

That's what I was thinking!. There's a lot of answers with things you can try to lower the noise. Dead silent is impossible! :icon_mrgreen: but you haven't show us the layout or measurements or anything to get some info about. If you're using the circuit that you showed before try to improve the filtering and the signal level. If you don't want to share the layout you can send it via PM and I have a look at it.

ok I read everything, now as I wrote at the beginning of the thread, the noise can be eliminated, but there is no concrete clarity on how to do it, they are all said assumptions, nobody published anything that says this has no noise, I guarantee it! And the one who has it, I don't know if he will share it clearly because it is a job and it is a challenge to do it.

No one can tell you "do this and the noise will go away" if we don't know where the noise is really came from and how big it is. As I tell you, there's a lot of options stated in the thread you can (and have!) to try to lower the noise.

The SN ratio is really good in the FV1 if you follow those steps. I have a bunch of old PCB's (professionaly manufactured) that have mistakes on the layout and get ground loops so there's a lot of noise, and other designs that are really silent with the propper techniques applied, same circuit in both cases.
Title: Re: FV SPIN - NOISE
Post by: octfrank on July 19, 2021, 06:30:46 PM
This is at least the third thread he has started on noise, he created two on the Spin forum last year. He has been provided solutions which he constantly rejects and never provides any measurements, PCB layouts, etc. I consider him a troll on the Spin forum now and while I have not blocked him there I really don't respond to him either.

I've only commented on the thread here because there are some really good suggestions that may help others that will listen and provide the necessary info to get help. And there is a post on the Spin forum http://www.spinsemi.com/forum/viewtopic.php?f=2&t=868 (http://www.spinsemi.com/forum/viewtopic.php?f=2&t=868) that does a nice job summarizing some great suggestions.
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 19, 2021, 08:58:59 PM
This is at least the third thread he has started on noise, he created two on the Spin forum last year. He has been provided solutions which he constantly rejects and never provides any measurements, PCB layouts, etc. I consider him a troll on the Spin forum now and while I have not blocked him there I really don't respond to him either.

I've only commented on the thread here because there are some really good suggestions that may help others that will listen and provide the necessary info to get help. And there is a post on the Spin forum http://www.spinsemi.com/forum/viewtopic.php?f=2&t=868 (http://www.spinsemi.com/forum/viewtopic.php?f=2&t=868) that does a nice job summarizing some great suggestions.


Look frank wrote here, because in your forum, you close the topics and you can't talk anymore, what you do is not very democratic.

I have always said that the fv spin is great, however it is very easy to have noise with it, I am not talking about my designs, I am talking about "professional" and recognized brands that have their product for sale, and when you turn it on you have a lot of noise there, then it is not a problem of my designs, the fv spin has noise and that's it.
It does not mean that it is bad, I have never said that, I said that the possible solutions you give, most do not change anything. Ldo regulator does nothing, ground on one side, does nothing, and so several other things that have been said, as they said above, the design of the pcb can surely make a big difference, but that is why it said to show with images, giving tips how to do it, it would be great for the product and that's what I mean, you say I refuse the indications? Why would I refuse if they are helping me? I tried everything and that's why I ask again, I do not demand anything, I only ask and if someone helps me great, that is only the end of this.
Anyone who starts working with this, has more breath than katrina, and when you start looking for possible solutions, most of them are not effective, then there are many technicalities that require much more knowledge, so if you know what I'm talking about, I was wondering because initially there are no schematics, or help to avoid all those hours of work with noise filtering.
But for you to understand once again, first I tell you that troll will be your sister ...  :icon_mrgreen: I'm not! I have only told my position and my problems with all this, I am sorry if it bothers you, it is not the purpose of generating a problem for you, I only want to achieve something good and decent. Now what is a decent sound? There is nothing written about tastes, so I can be me, too demanding with something that I don't know if he ever gave me what I'm looking for.

Look, finally I tell you that it is full of pedals with the pt2399 and I would never use it, so that responds to many things.

If the administrator prefers it, delete the post and that's it, it is not the idea to generate any conflict or damage the image of the product, because once again I say, that for me it is EXCELLENT, but complicated to achieve something of a good level, at the Except that happens to me and more than 10 people that I have spoken with and do things with this, the difference is that they relax and do not give it importance, I can not. sorry!

Title: Re: FV SPIN - NOISE
Post by: niektb on July 20, 2021, 01:42:12 AM
Well, that's not really constructive... Calling each other names...
Still I tend to agree with Octfrank, you're mainly reiterating your own words without giving any kind of factual info that we can go on. What are you listening to? How bad is it really? How did you decide that it's the pedal with the FV-1 that's too noisy. Can you give audio examples? (For the noisy case, but also for the improved case?) What schematics are we currently talking about? (As you said you tried different solutions)

most of us don't recognize your problem but you're not even trying to give a detailed explanation. Please do so we can get to the bottom of this  :icon_razz: or, if you're not willing to, otherwise I would suggest to just completely stop this topic because this is not going anywhere in the current psce :)
Title: Re: FV SPIN - NOISE
Post by: Blackaddr on July 20, 2021, 09:04:15 AM
AndyF, there are tons of boutique pedals based around the FV-1 that are not unacceptably noisy for pedals costing a few hundred dollars. There are also a lot of amateurish pedals that do have noise and interference issues and it often has nothing to do with the schematic and everything to do with the PCB layout.

The dB noise spec for the FV-1 is in the 90s. That is very good, but it's very difficult to achieve from end to end across a circuit board without a very careful PCB design. Total SNR in the high 60s end-to-end most people would still find acceptable for a guitar pedal. SNR in the 30 and 40s is where most people would complain about a pedal being unacceptably noisy.

If you are getting unusually poor SNRs the two most likely situations are:

1) The PCB design does not employ sufficient PCB design techniques such as ground and power plane shielding, isolation of analog from digital sections, current steering cutouts, and reduction of cross talk (no parallel aggressor/victim tracks).

2) One or more of the ESD sensitive components on the board have been damaged by static discharge.

My advice:
1) measure your SNR, if you're getting 80 dB and it's still unacceptable to you, you have golden ears. If it's in the 30s or 40s, your PCB layout has issues.
2) Build a second board following strict ESD procedures to determine if you've damaged your parts with static at some point.
2) go find some online resources or courses on 'mixed-signal design' and do an improved PCB design.
Title: Re: FV SPIN - NOISE
Post by: octfrank on July 20, 2021, 11:00:20 AM
Well, that's not really constructive... Calling each other names...

And you are correct, I just didn't know of another way to describe my opinion as this started a year ago on the Spin forum and in that time he is yet to provide a single measurement or PCB layout. At some point I just determined he is intentionally wasting peoples' time,  I would like to be proved wrong and have him post actual data that may assist others but I don't believe that will ever happen.
 
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 20, 2021, 11:04:12 AM
AndyF, there are tons of boutique pedals based around the FV-1 that are not unacceptably noisy for pedals costing a few hundred dollars. There are also a lot of amateurish pedals that do have noise and interference issues and it often has nothing to do with the schematic and everything to do with the PCB layout.

The dB noise spec for the FV-1 is in the 90s. That is very good, but it's very difficult to achieve from end to end across a circuit board without a very careful PCB design. Total SNR in the high 60s end-to-end most people would still find acceptable for a guitar pedal. SNR in the 30 and 40s is where most people would complain about a pedal being unacceptably noisy.

If you are getting unusually poor SNRs the two most likely situations are:

1) The PCB design does not employ sufficient PCB design techniques such as ground and power plane shielding, isolation of analog from digital sections, current steering cutouts, and reduction of cross talk (no parallel aggressor/victim tracks).

2) One or more of the ESD sensitive components on the board have been damaged by static discharge.

My advice:
1) measure your SNR, if you're getting 80 dB and it's still unacceptable to you, you have golden ears. If it's in the 30s or 40s, your PCB layout has issues.
2) Build a second board following strict ESD procedures to determine if you've damaged your parts with static at some point.
2) go find some online resources or courses on 'mixed-signal design' and do an improved PCB design.

thanks for your recommendations and suggestions.
Title: Re: FV SPIN - NOISE
Post by: AndyF on July 20, 2021, 11:20:12 AM
Well, that's not really constructive... Calling each other names...

And you are correct, I just didn't know of another way to describe my opinion as this started a year ago on the Spin forum and in that time he is yet to provide a single measurement or PCB layout. At some point I just determined he is intentionally wasting peoples' time,  I would like to be proved wrong and have him post actual data that may assist others but I don't believe that will ever happen.


Don't worry, frank, do you think it's something to annoy you or that my intention is to speak ill of a product, which I always say is great, why do you only read what you think?
I do not understand how you have me so present ...
As I said before, my doubts were amplified when I tried pedals of recognized brands and they had the same noise and I understood that it could be something more than my pcbs.
Now I am clear that it can be removed or filtered, if someone did, then it can. I was just looking for helpful tips ...
I do not usually write in the forums, I do not have much to contribute unfortunately, I just made a query, thinking that someone else would go through the same thing and give me some good indication, there is nothing more than this.
Sure the problem must be mine, do not worry I will not write more and I will not say anything else, it does not make sense. It works great for all of them and only I have noise, it is clear that I have the problem.

To clear all your doubts, I tell you that my intention is not to bother, my intention is not to speak ill of a product that I see great, my intention is to try to solve this with my little knowledge and with some tip that works, nothing more for say.

I apologize if I disturb you or someone else, anything I said.
Title: Re: FV SPIN - NOISE
Post by: mark2 on January 14, 2022, 11:12:01 AM
The dB noise spec for the FV-1 is in the 90s. That is very good, but it's very difficult to achieve from end to end across a circuit board without a very careful PCB design. Total SNR in the high 60s end-to-end most people would still find acceptable for a guitar pedal. SNR in the 30 and 40s is where most people would complain about a pedal being unacceptably noisy.

...

1) measure your SNR, if you're getting 80 dB and it's still unacceptable to you, you have golden ears. If it's in the 30s or 40s, your PCB layout has issues.

What's an appropriate way to measure SNR?

e.g. I can estimate the standalone noise to be (from memory, maybe not accurate) 140mV peak-to-peak by disconnecting the input signal and looking at the scope. But I'm not sure how to isolate the noise from the signal in the combined output.
Title: Re: FV SPIN - NOISE
Post by: ElectricDruid on January 14, 2022, 03:35:13 PM
What's an appropriate way to measure SNR?

Yeah, it's sometimes tricky. Perhaps especially when the levels get very low.

I've been working on and off trying to reduce the noise level caused by clock jitter in my Flangelicious design. There's a certain level of "watery" background noise that's caused by that, and I'd like to try and reduce it. But first I have to measure it. That's not that simple, since the actual level of that noise varies depending on the clock frequency. What I'd like is some sort of measure of "overall noise level across the whole clock frequency sweep" but that's not at all an easy thing to get a figure on. And because we're talking about jitter, the amount at any particular frequency can vary enormously from another frequency very close, so measurements at specific points don't tell us too much.
So how would I quantify the background noise level, and furthermore how would I quantify it over a whole range of output clock frequencies?

Going back to the problem at hand, I don't think this is that difficult. The FV-1 can be set up with a straight input-to-output algorithm, which should show only the noise introduced by the ADC-DAC process. You can then ground the input to eliminate noise going in. If you also eliminate the dry signal from the output, then what you're looking at is noise caused by the PCB layout and whatever other circuitry there is on the board. That's a fairly clear measure of the background noise level of the circuit. If the noise goes up horribly when it's running a specific algorithm, then the suspicion clearly has to fall on the algorithm, not the rest of the board.

HTH,
Tom



Title: Re: FV SPIN - NOISE
Post by: octfrank on January 16, 2022, 11:30:27 AM

What's an appropriate way to measure SNR?

e.g. I can estimate the standalone noise to be (from memory, maybe not accurate) 140mV peak-to-peak by disconnecting the input signal and looking at the scope. But I'm not sure how to isolate the noise from the signal in the combined output.

Honestly you need a spectrum analyzer as you need to add all the noise in the range of interest (20Hz to Fs/2) so an FFT is required. In addition there must be a reference signal at say -6db that is centered in one of the FFT bins. You eliminate this bin in calculating the noise floor for SNR, if you cannot do so in the spectrum analyzer then use a notch filter.

If you have a digital scope it may have some basic FFT capabilities so you can do a simple measurement with a notch filter to eliminate the reference signal.

You need a really pure sine wave as any distortion can raise the noise floor due to the reference signal which means you are not getting a good measure.

What may help more is a digital scope with FFT, put in a reference sine centered on a bin and look for peaks in other bins that indicate issues in the circuit/PCB.

A nice simple example is here https://itectec.com/electrical/electronic-how-to-measure-snr-with-an-oscilloscope/ (https://itectec.com/electrical/electronic-how-to-measure-snr-with-an-oscilloscope/)
Title: Re: FV SPIN - NOISE
Post by: mark2 on January 18, 2022, 01:58:19 PM
Thanks Frank and Tom,

This helps a lot. I'll definitely start with the simpler method.
Failing that (or just to explore further) I'll try the FFT method as well. My signal generator is pretty crude, but I can probably figure out something.
Title: Re: FV SPIN - NOISE
Post by: MetalGuy on January 18, 2022, 04:02:31 PM
Since this thread is still going on I decided to check again my unit for FV-1 noise. Usually if I need to check something for noise I connect it to the Return stage of my 100W tube head and put the Master to max. No noise can escape from that.
With my unit at idle (input0 to gnd, in a quiet room, 1 meter from the speakers) I can't hear any extra noise whatsoever from the unit. With some effects engaged I can barely hear the LFOs. Note that with the Master at max the amp would produce deafening volumes when played so for my purposes the noise from my FV-1 unit is insignificant (if at all).