@Cmaj7 said:

By the way, one related question regarding the implementation: are there performance differences between implementations with lots of [f ], [+ ], [t b f], etc ... and a simple [expr] or [expr~] ? Is one way preferable?

Whithout any proof I will say this: when you load [expr] you load a shitload of functions in one object. I don't need pow, exp, sqrt, whatnot in order to do a linear transformation with 2-3 objects. You are also loading an "extra" which is not always supported in ports like libpd/mobmuplat depending on platform and version

@jameslo - I am aware of the extended objects but I stick to vanilla for various reasons ([init~] is not loading here).

[cos~] provides a nice soft and smooth distortion for synth sounds- I use it a lot to beef up bass and snare etc, but usually only one pass and with a dry/wet crossfader to adjust amount. The way it's subtle also makes it good for exciter effects. Example:
exciter~.pd

You could of course change the filter, add more passes, try other sigmoids for the sound you want.

To stay on topic, here's a sigmoid based on the [pow~] object, using some convoluted math to allow asymmetric distortion curves (bias): pow-sigmoid~.pd

@Cmaj7 there is an old discussion of the mtof (and ftom) math here: https://forum.pdpatchrepo.info/topic/4090/midi-to-hz-and-hz-to-midi-formulas/ - pay attention to @seb-harmonik-ar and @gsagostinho 's answers

The mtof formula written in simple math is F = 440 x 2^((M-69)/12) or [expr 440*(pow (2, (($f1-69)/12)))] in pd lingo. It's not a superexponential (sorry @ddw_music I do agree on getting the mapping right tho). The 440 and 69 are sort of arbitrary in that they set a reference of Hz/Midnumber. You could just as well use 220 and 57 or any other pair you know to be correct, although keeping them sort of close to middle C is probably a good idea...

It's hard to tell without knowing your setup. OS? Hardware?

I run PD vanilla on xubuntu 20.?? (latest LTS) and an external sound card/mixer (cheap behringer). I can get audio both with and without jack

If I set up PD to run just with ALSA (no jack) and I have some other programs running that are using the sound card (like a browser or whatever) PD will tell me:

ALSA input error (snd_pcm_open): No such file or directory
ALSA output error (snd_pcm_open): No such file or directory

However, closing my browser and/or other programs that route sound through ALSA solves this

Using jack instead gives me the advantage of running other DAW software along side PD and route both midi and audio back and forth between them (non jack programs will be silenced), but jack has to be set up properly for the server to run without dropouts (select the correct soundcard, buffer size etc in settings), or even start at all. For this purpose I use qjackctl, which is a GUI control panel for the jack server- should be in your distro's repositories.

The errors you get with jack simply states that the jack server is not running- it has to be started manually. You can do that with a command from your terminal or get the qjackctl software for the GUI (which I reckon you will prefer as a windows convert). Run: sudo apt install qjackctl from your terminal to install it if you are using a debian based distro (*ubuntu, mint et al)

The expr family has been part of vanilla PD for a long time, so I would assume they are included in libpd?

If not have a look at this: https://github.com/libpd/libpd/wiki/Adding-Pure-Data-external-libraries-to-your-project

Sorry to be a hair-splitter here, but the assignment in the OP clearly says:

"Create a glissando that we hear as linear and one that we hear as logarithmic from C3 to C6."

What we hear as a linear sweep is a log sweep: we perceive the same distance from A3 (220hz) to A4 (440hz) as we do from A4 (440hz) to A5 (880hz), while in reality the latter is twice as long as the former.

Hence, what we will hear as a linear sweep is @seb-harmonik.ar 's solution, while a linear upwards sweep like the one in OP's patch will sound as if it's slowing down exponentially - whether that qualifies as "hearing it as a logarithmic sweep" I will leave to the math geeks to ascertain

My friend is using PD on an rpi as an effects processor for his guitar and has been trying out various simple distortion methods so I sat down and made a sigmoid abstraction for him with adjustable knee, kinda basic but nice sounding...

sigmoid~.pd
sigmoid~-help.pd

I am posting it here as I am curious as to what kinds of sigmoid solutions you guys have up your sleeve. So let's dedicate this thread to sharing homebrew sigmoids

@jameslo you still win this round

You are only passing bangs to the two [f] objects. Try this:

EDIT: Scrap that. It wont work as intended. Pd will print 0 0 when you bang the inlet

@jameslo Eureka!

But if the [+ } increment caused the counter to never land on 3, then it would never reset.

The select output that triggers the reset is the last one i.e anything but 0 1 2 3, so not an issue