[Csnd-dev] Why does the portk opcode not accept a negative isig?

[Csnd-dev] Why does the portk opcode not accept a negative isig?

Date	2022-06-05 01:40
From	andy fillebrown
Subject	[Csnd-dev] Why does the portk opcode not accept a negative isig?
	I'm trying to use the pork opcode with a negative isig but the internal feedback value is not being set. It only gets set if the value is greater than or equal to zero. See https://github.com/csound/csound/blob/2e324328d0bf8b446b6c20082224de311982c4bb/OOps/ugens5.c#L41-L42.

Date	2022-06-05 11:33
From	Eduardo Moguillansky
Subject	Re: [Csnd-dev] Why does the portk opcode not accept a negative isig?
Attachments	portk-lag-comp.csd
	This looks like a bug in the code. Since isig defaults to 0 when not passed, the initial state should always be set to the isig value. You can always use the lag opcode instead, which allows to ramp from any value, and if not given an initial value, it ramps from the first value of ksig (this is often what you want). lag is almost a drop-in replacement, the only difference being that the lagtime is calculated differently, so for "lag" you should multiply the value passed to port by a factor of ~8.6 to replicate the exact ramp curve of port. Run the attached .csd in csoundqt to see a plot of "port" against "lag" On 05.06.22 02:40, andy fillebrown wrote: > I'm trying to use the pork opcode with a negative isig but the > internal feedback value is not being set. It only gets set if the > value is greater than or equal to zero. > > See https://github.com/csound/csound/blob/2e324328d0bf8b446b6c20082224de311982c4bb/OOps/ugens5.c#L41-L42. > > Why is a negative isig skipped in the code?

Date	2022-06-05 13:56
From	andy fillebrown
Subject	Re: [Csnd-dev] Why does the portk opcode not accept a negative isig?
	Thank you. I will use the lag opcode instead. On Sun, Jun 5, 2022 at 6:33 AM Eduardo Moguillansky wrote: > > This looks like a bug in the code. Since isig defaults to 0 when not > passed, the initial state should always be set to the isig value. > > You can always use the lag opcode instead, which allows to ramp from any > value, and if not given an initial value, it ramps from the first value > of ksig (this is often what you want). lag is almost a drop-in > replacement, the only difference being that the lagtime is calculated > differently, so for "lag" you should multiply the value passed to port > by a factor of ~8.6 to replicate the exact ramp curve of port. > > Run the attached .csd in csoundqt to see a plot of "port" against "lag" > > > On 05.06.22 02:40, andy fillebrown wrote: > > I'm trying to use the pork opcode with a negative isig but the > > internal feedback value is not being set. It only gets set if the > > value is greater than or equal to zero. > > > > See https://github.com/csound/csound/blob/2e324328d0bf8b446b6c20082224de311982c4bb/OOps/ugens5.c#L41-L42. > >

Date	2022-06-05 20:34
From	John ff
Subject	Re: [Csnd-dev] Why does the portk opcode not accept a negative isig?
	That definition of portk dates back to before 1988 so that has been incorrectly documented. I believe the intent is to be able to start from a previous instantiation if the filter if using us negative. ==John ff Get TypeApp for Android On 5 Jun 2022, at 11:34, Eduardo Moguillansky <eduardo.moguillansky@gmail.com> wrote: This looks like a bug in the code. Since isig defaults to 0 when not passed, the initial state should always be set to the isig value. You can always use the lag opcode instead, which allows to ramp from any value, and if not given an initial value, it ramps from the first value of ksig (this is often what you want). lag is almost a drop-in replacement, the only difference being that the lagtime is calculated differently, so for "lag" you should multiply the value passed to port by a factor of ~8.6 to replicate the exact ramp curve of port. Run the attached .csd in csoundqt to see a plot of "port" against "lag" On 05.06.22 02:40, andy fillebrown wrote: I'm trying to use the pork opcode with a negative isig but the internal feedback value is not being set. It only gets set if the value is greater than or equal to zero. See https://github.com/csound/csound/blob/2e324328d0bf8b446b6c20082224de311982c4bb/OOps/ugens5.c#L41-L42. Why is a negative isig skipped in the code?

Date	2022-06-05 22:58
From	Victor Lazzarini
Subject	Re: [Csnd-dev] [EXTERNAL] Re: [Csnd-dev] Why does the portk opcode not accept a negative isig?
	yes. The code checks for isig >= 0 and uses it, otherwise the value stored is kept. if (LIKELY(p->isig >= FL(0.0))) p->yt1 = (double)(p->isig); It's not a bug, it's what it's supposed to do. The normal use of port/portk is with non-negative input, and so it was designed to have a means to preserve the value from a previous instance. If the manual needs to be corrected, then it should. Prof. Victor Lazzarini Maynooth University Ireland On 5 Jun 2022, at 20:35, John ff <jpff@codemist.co.uk> wrote: Warning This email originated from outside of Maynooth University's Mail System. Do not reply, click links or open attachments unless you recognise the sender and know the content is safe. That definition of portk dates back to before 1988 so that has been incorrectly documented. I believe the intent is to be able to start from a previous instantiation if the filter if using us negative. ==John ff Get TypeApp for Android On 5 Jun 2022, at 11:34, Eduardo Moguillansky <eduardo.moguillansky@gmail.com> wrote: This looks like a bug in the code. Since isig defaults to 0 when not passed, the initial state should always be set to the isig value. You can always use the lag opcode instead, which allows to ramp from any value, and if not given an initial value, it ramps from the first value of ksig (this is often what you want). lag is almost a drop-in replacement, the only difference being that the lagtime is calculated differently, so for "lag" you should multiply the value passed to port by a factor of ~8.6 to replicate the exact ramp curve of port. Run the attached .csd in csoundqt to see a plot of "port" against "lag" On 05.06.22 02:40, andy fillebrown wrote: I'm trying to use the pork opcode with a negative isig but the internal feedback value is not being set. It only gets set if the value is greater than or equal to zero. See https://github.com/csound/csound/blob/2e324328d0bf8b446b6c20082224de311982c4bb/OOps/ugens5.c#L41-L42. Why is a negative isig skipped in the code?