Translate db_to_gain before smoothing the parameter

[BillyDM]

You should definitely add the ability for a parameter to translate its value using util::db_to_gain before smoothing it.

The current gain example is woefully inefficient since it is converting from db to gain every single sample:

for channel_samples in buffer.iter_samples() {
    // Smoothing is optionally built into the parameters themselves
    let gain = self.params.gain.smoothed.next();

    for sample in channel_samples {
        *sample *= util::db_to_gain(gain);
    }
}

This is how baseplug implements this: https://github.com/wrl/baseplug/blob/trunk/src/parameter.rs#L116

[BillyDM]

Essentially I'm saying that the actual parameter should store its value in raw amplitude, and only do the translation between db and amplitude when interacting with the UI/host.

[BillyDM]

(Sorry for all the title changes, lol. I kept thinking there was more to add when looking at the code, but then I realized it was fine).

[robbert-vdh]

This is intentional. Check out the other non-example plugins in the repo. The examples have gain parameters in the logarithmic domain, while the non-example plugins have the parameters in linear space using formatters::{v2s,s2v}_f32_gain_to_db and util::db_to_gain for ranges. In these example plugins you really won't notice the DSP load difference from one extra powf per sample and I think it mamkes everything a bit clearer. I should probably change at least one of the examples to have linear gain parameters though just to show off how to use those formatters.

[BillyDM]

Ah, I see. That makes perfect sense. Thanks for the help!

[robbert-vdh]

But thanks for bringing this to my attention! I'll probably update the gain example and leave the sine example alone because showing off those formatters is probably also a good idea. (so I'm reopening this issue as a reminder for myself 😄)

[robbert-vdh]

Okay, the basic and GUI gain examples now use linear gain to show off all of the utilities there. Makes things more complex, but it's probably good to show this off. There's a new FloatRange::gain_skew_factor(min_db, max_db) function that can be used together with FloatRange::Skewed to make the gain range appear as if it is linear on a decibel/logarithmic scale.