Doepfer

--- In Doepfer_a100@yahoogroups.com, "isoldeandisobelle"  wrote:
>
> Hi,
> 
> If I take the output (without any input)from my A-107 and feed it into my A-138B mixer, a constant noise can be heard, like the sound of a noise generator,this is louder on some filter presets than others.
> If this signal is fed through a VCA, then the sound is, as to be expected, much louder....the sound is also there when the filter is receiving a sound source.....any suggestions, please.
> 
> 
> Kind regards
>
Hi,

Any help with this?

I had already returned this module to my place of purchase, who passed it on to Doepfer, as it was producing the same ''noise'' sound but also was faulty in that every filter was not operating correctly, and was kindly replaced once tested.

Thank you

--- In Doepfer_a100@yahoogroups.com, Florian Anwander  wrote:
>
> Hello
> 
> it is difficult to judge for us. Maybe you should post record an example 
> on soundcloud so we can tell you whether it is normal or not.
> 
> Record first the filteroutput with a simple sawtooth and then (without 
> changing the level) the filter-noise without any input signal.
> 
> Florian
> 
> 
> On 13.02.13 19:58 , isoldeandisobelle wrote:
> >
> >
> > --- In Doepfer_a100@yahoogroups.com, "isoldeandisobelle"  wrote:
> >>
> >> Hi,
> >>
> >> If I take the output (without any input)from my A-107 and feed it into my A-138B mixer, a constant noise can be heard, like the sound of a noise generator,this is louder on some filter presets than others.
> >> If this signal is fed through a VCA, then the sound is, as to be expected, much louder....the sound is also there when the filter is receiving a sound source.....any suggestions, please.
> >>
> >>
> >> Kind regards
> >>
> > Hi,
> >
> > Any help with this?
> >
> > I had already returned this module to my place of purchase, who passed it on to Doepfer, as it was producing the same ''noise'' sound but also was faulty in that every filter was not operating correctly, and was kindly replaced once tested.
> >
> > Thank you
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>
Hi,

Thank you for your reply.

Here is the soundcloud link - https://soundcloud.com/isolde-and-isobelle/a-107

First with a sawtooth and then just the filter out as I turn through the filter presets....it is also more noticeable with something like a sine.

Best wishes

Hello

it is difficult to judge for us. Maybe you should post record an example 
on soundcloud so we can tell you whether it is normal or not.

Record first the filteroutput with a simple sawtooth and then (without 
changing the level) the filter-noise without any input signal.

Florian

On 13.02.13 19:58 , isoldeandisobelle wrote:
>
>
> --- In Doepfer_a100@yahoogroups.com, "isoldeandisobelle"  wrote:
>>
>> Hi,
>>
>> If I take the output (without any input)from my A-107 and feed it into my A-138B mixer, a constant noise can be heard, like the sound of a noise generator,this is louder on some filter presets than others.
>> If this signal is fed through a VCA, then the sound is, as to be expected, much louder....the sound is also there when the filter is receiving a sound source.....any suggestions, please.
>>
>>
>> Kind regards
>>
> Hi,
>
> Any help with this?
>
> I had already returned this module to my place of purchase, who passed it on to Doepfer, as it was producing the same ''noise'' sound but also was faulty in that every filter was not operating correctly, and was kindly replaced once tested.
>
> Thank you
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>

On 13.02.13 22:17 , isoldeandisobelle wrote:
> Here is the soundcloud link - https://soundcloud.com/isolde-and-isobelle/a-107
>
> First with a sawtooth and then just the filter out as I turn through the filter presets....it is also more noticeable with something like a sine.
I don't own a A_107, but I even could imagine, that this is the normal 
noise level at certain filtersettings. Especially if high pass filters 
are placed as last part of the filteralgorithm. Dieter may jump in here. 
Perhaps the bandpasses are generated using LP->HP instead of HP->LP.

Florian

Well, Ok, Thank you for your reply.

If you say this is a normal level for this unit, then that is fine with me, I did not want it to be a fault that became progressively louder within time.

Best wishes to all and thanks again for your advice.
--- In Doepfer_a100@yahoogroups.com, Florian Anwander  wrote:

>
> On 13.02.13 22:17 , isoldeandisobelle wrote:
> > Here is the soundcloud link - https://soundcloud.com/isolde-and-isobelle/a-107
> >
> > First with a sawtooth and then just the filter out as I turn through the filter presets....it is also more noticeable with something like a sine.
> I don't own a A_107, but I even could imagine, that this is the normal 
> noise level at certain filtersettings. Especially if high pass filters 
> are placed as last part of the filteralgorithm. Dieter may jump in here. 
> Perhaps the bandpasses are generated using LP->HP instead of HP->LP.
> 
> Florian
>

Am 14.02.2013 18:08, schrieb isoldeandisobelle:
> If you say this is a normal level for this unit, then that is fine with me,
I don't know whether it is normal! I do not own a 107.

But, I can *imagine* that it is normal.

Thank you for your replies Florian, perhaps Dieter will have the definitive answer.

--- In Doepfer_a100@yahoogroups.com, Florian Anwander <fanwander@...> wrote:

>
> Am 14.02.2013 18:08, schrieb isoldeandisobelle:
> > If you say this is a normal level for this unit, then that is fine with me,
> I don't know whether it is normal! I do not own a 107.
> 
> But, I can *imagine* that it is normal.
>

> Thank you for your replies Florian, perhaps Dieter will have the
> definitive answer.

I don't know the "definitive answer" but indeed the XP filter design
generates a bit more noise than other filters (the A-107 is nothing but an
expanded XP filter). The reason is that the original signals of the four
filter stages (CEM3379 filter chip) have very low levels and have to be
amplified by about 100 to obtain the audio level used in the A-100. This
causes a higher noise floor because even the noise is amplified. And in
addition some filter types are composed from up to 4 filter stages. This
increases the noise additionally. The filter types that use only one filter
stage (i.e. 6, 12, 18, 24 dB low pass) should be a bit less noisy because
for these only one of the filter stages is used.

But with max. audio input level (i.e. just before clipping) the noise floor
should cause no problems.

Best wishes
Dieter Doepfer

That is definitive enough for me, thank you very much.
Yes, it is not too much of a problem, as with higher inputs the noise is all but suppressed or masked and with the filter types you mentioned it is not at all so bad, only in the quieter passages that I may create does it become a bit of an issue, but then I tend to just use another filter module for those parts.

I was only concerned that it may have been a fault that may have got progressively louder over time.....but, your answer puts that worry aside.

Thank you again and best wishes.
--- In Doepfer_a100@yahoogroups.com, <yahoo@...> wrote:

>
> > Thank you for your replies Florian, perhaps Dieter will have the
> > definitive answer.
> 
> I don't know the "definitive answer" but indeed the XP filter design
> generates a bit more noise than other filters (the A-107 is nothing but an
> expanded XP filter). The reason is that the original signals of the four
> filter stages (CEM3379 filter chip) have very low levels and have to be
> amplified by about 100 to obtain the audio level used in the A-100. This
> causes a higher noise floor because even the noise is amplified. And in
> addition some filter types are composed from up to 4 filter stages. This
> increases the noise additionally. The filter types that use only one filter
> stage (i.e. 6, 12, 18, 24 dB low pass) should be a bit less noisy because
> for these only one of the filter stages is used.
> 
> But with max. audio input level (i.e. just before clipping) the noise floor
> should cause no problems.
> 
> Best wishes
> Dieter Doepfer
>