Denormal Prevention

How bbx_audio handles denormal floating-point numbers.

What are Denormals?

Denormal (subnormal) numbers are very small floats near zero:

Normal:   1.0e-38   (exponent > 0)
Denormal: 1.0e-40   (exponent = 0, mantissa != 0)

The Problem

Processing denormals causes severe CPU slowdowns:

• 10-100x slower operations
• Unpredictable latency spikes
• Common in audio (decaying signals)

Flush Functions

bbx_core provides flush utilities:

#![allow(unused)]
fn main() {
use bbx_core::{flush_denormal_f32, flush_denormal_f64};

let safe = flush_denormal_f32(maybe_denormal);
}

When They Occur

• Filter feedback paths (decaying)
• Reverb/delay tails
• After gain reduction
• Envelope release phase

Usage in Blocks

Apply in feedback paths:

#![allow(unused)]
fn main() {
fn process_filter(&mut self, input: f32) -> f32 {
    let output = input + self.state * self.coefficient;
    self.state = flush_denormal_f32(output);
    output
}
}

Alternative Approaches

CPU FTZ/DAZ Mode

bbx_core provides the ftz-daz Cargo feature for hardware-level denormal prevention. When enabled, the enable_ftz_daz() function sets CPU flags to automatically flush denormals to zero.

Enable the feature in your Cargo.toml:

[dependencies]
bbx_core = { version = "...", features = ["ftz-daz"] }

# Or for plugins (recommended):
bbx_plugin = { version = "...", features = ["ftz-daz"] }

Usage:

#![allow(unused)]
fn main() {
use bbx_core::denormal::enable_ftz_daz;

// Call once at the start of each audio thread
enable_ftz_daz();
}

When using bbx_plugin with the ftz-daz feature, this is called automatically during prepare().

Platform Support

Note: ARM processors lack a universal DAZ equivalent, so denormal inputs are handled normally. For portable code, use flush_denormal_f32/f64 in filter feedback paths as defense-in-depth.

DC Offset

Add tiny DC offset to prevent zero crossing:

#![allow(unused)]
fn main() {
const DC_OFFSET: f32 = 1e-25;
let output = (input + DC_OFFSET) * coefficient;
}

Pros: Simple, portable Cons: Introduces actual DC offset