Hi there,

Is the Csound 'reson' unit a resonant lowpass filter in the traditional
subtractive synthesis sense?  What's the relationship between the
notions of 'center frequency' and 'bandwidth' and the traditional
'cutoff' and 'resonance' controls on analog synthesizers?  Is it
possible to translate between a 0-100% resonance control and the kbw
parameter accepted by reson, with equivalent output?  -- and
equivalently for the kcf parameter?

I am reading through the filters section of the Audio Programming Book
and the code for the resonator filter demonstrated there is named
'bandpass()' and doesn't seem to implement the corresponding Butterworth
coefficients for the lowpass filter -- rather it's closer to the
bandpass coefficients (although none of the 4 shapes seem to exactly
match the algorithm?)

Therefore I would assume that 'reson' is also a bandpass filter, unless
the 'type' of filter (LP, HP, BP, BR) is not hard-wired into the
algorithm but can be varied with values of kcf and kbw?  Is there any
useful sample C code for a resonant lowpass filter, along the same lines
as the resonator() example from TAPB?  I guess I can read the source of
units like 'rezzy' etc, but I am after a very standard and literal
implementation without any unit-specific customizations.

Cheers,
Dave

The reson source is in OOps/ugens5.c.

On 12/26/13, David Banks  wrote:
> Hi there,
>
> Is the Csound 'reson' unit a resonant lowpass filter in the traditional
> subtractive synthesis sense?  What's the relationship between the
> notions of 'center frequency' and 'bandwidth' and the traditional
> 'cutoff' and 'resonance' controls on analog synthesizers?  Is it
> possible to translate between a 0-100% resonance control and the kbw
> parameter accepted by reson, with equivalent output?  -- and
> equivalently for the kcf parameter?
>
> I am reading through the filters section of the Audio Programming Book
> and the code for the resonator filter demonstrated there is named
> 'bandpass()' and doesn't seem to implement the corresponding Butterworth
> coefficients for the lowpass filter -- rather it's closer to the
> bandpass coefficients (although none of the 4 shapes seem to exactly
> match the algorithm?)
>
> Therefore I would assume that 'reson' is also a bandpass filter, unless
> the 'type' of filter (LP, HP, BP, BR) is not hard-wired into the
> algorithm but can be varied with values of kcf and kbw?  Is there any
> useful sample C code for a resonant lowpass filter, along the same lines
> as the resonator() example from TAPB?  I guess I can read the source of
> units like 'rezzy' etc, but I am after a very standard and literal
> implementation without any unit-specific customizations.
>
> Cheers,
> Dave
>
>
>
> Send bugs reports to the Sourceforge bug trackers
> csound6:
>             https://sourceforge.net/p/csound/tickets/
> csound5:
>             https://sourceforge.net/p/csound/bugs/
> Discussions of bugs and features can be posted here
> To unsubscribe, send email sympa@lists.bath.ac.uk with body "unsubscribe
> csound"
>
>
>

Reson is not a lowpass but a bandpass filter. It’s a digital filter that is not directly modelled by an analog counterpart
(unlike the butterworth). The “bandpass” filter in the Audio Programming Book is a reson variant that includes a feedforward
path, and is equivalent (afaik) to resonz in Csound.

Victor

On 26 Dec 2013, at 16:25, David Banks  wrote:

> Hi there,
> 
> Is the Csound 'reson' unit a resonant lowpass filter in the traditional
> subtractive synthesis sense?  What's the relationship between the
> notions of 'center frequency' and 'bandwidth' and the traditional
> 'cutoff' and 'resonance' controls on analog synthesizers?  Is it
> possible to translate between a 0-100% resonance control and the kbw
> parameter accepted by reson, with equivalent output?  -- and
> equivalently for the kcf parameter?
> 
> I am reading through the filters section of the Audio Programming Book
> and the code for the resonator filter demonstrated there is named
> 'bandpass()' and doesn't seem to implement the corresponding Butterworth
> coefficients for the lowpass filter -- rather it's closer to the
> bandpass coefficients (although none of the 4 shapes seem to exactly
> match the algorithm?)
> 
> Therefore I would assume that 'reson' is also a bandpass filter, unless
> the 'type' of filter (LP, HP, BP, BR) is not hard-wired into the
> algorithm but can be varied with values of kcf and kbw?  Is there any
> useful sample C code for a resonant lowpass filter, along the same lines
> as the resonator() example from TAPB?  I guess I can read the source of
> units like 'rezzy' etc, but I am after a very standard and literal
> implementation without any unit-specific customizations.
> 
> Cheers,
> Dave
> 
> 
> 
> Send bugs reports to the Sourceforge bug trackers
> csound6:
>            https://sourceforge.net/p/csound/tickets/
> csound5:
>            https://sourceforge.net/p/csound/bugs/
> Discussions of bugs and features can be posted here
> To unsubscribe, send email sympa@lists.bath.ac.uk with body "unsubscribe csound"
> 
>