What *exactly* is a noise burst

[4516N41]

This may be a stupid observation but the VU meter does not detect the noiseburst.

No, that's very true - A lot of times I have noise bursts it shows up on the master VU meter as having an output of -inf db, or is that just the behaviour of Buzz representing >0db volume ?

(erm, or is than not what you meant )

I´m pretty sure we are on the same page

[UNZ]

yeah for +-inf values you have to account for, i did in mixio by just clipping the vu pixel values at +a few db over the max of the vu. i guess buzz's vu doesn't, so the calculation comes out as 0 pixels width.

the presence of those values indicates a bug somewhere btw.

[mcbpete]

So would it follow that (in rather simplistic coding terms) a possible check could be something along the lines of: if ((output != 0) && (buzz VU meter == 0)){noiseburst handler}

Or again would such a routine be completely impracticable?

[UNZ]

no that wont work hehe (for example, one shouldnt mix up gui and audio stuff randomly and the criteria is much too simple)

my post was just about the vu display btw, just a gui issue (caused by a bug somewhere in audio thread(s) tough, some machine fucks up, but the gui should be protected against those and other unreasonable values).

[Reefer Sutherland]

A previous machine in the chain could clip it to the range.

This makes sense of course

[cyanphase]

Noise bursts can happen from a few possible causes:

1. Sample buffers weren't zero'd before mixing waveforms onto them.
2. Accessed wrong memory.
3. Most often, maybe, all the time, an IIR filter went outside its safe ranges and went unstable, these filters become "broken" because they feed onto their immediate past to define their present.


About the noise burst detection:

Here is the noise burst heuristic that was used in Overloader. It keeps track of a "demerit" score based on delta and peak sample values.
Not sure if its a reasonable algorithm (maybe not, but it could be disabled or reset), its kinda simple, but please feel free to use it for any purpose, I set this noise burst protection code into the public domain for any use.

Code: Select all

float chprot_peak_threshold;
float chprot_delta_threshold;
int   chprot_silence_time;
int   chprot_silence_samples;
int   chprot_release_time;
int   chprot_release_samples;
float chprot_current_envelope;
int   chprot_current_env_period;
float post_last_sample;
float post_demerit;
// int   chprot_windowopen; // GUI
// int   chprot_windowaclose;


Initialize:

chprot_peak_threshold = 40000.0f;
chprot_delta_threshold = 10000.0f;
chprot_silence_time = 1000;
chprot_release_time = 100;
chprot_silence_samples = (chprot_silence_time * getSampleRate()) / 1000;
chprot_release_samples = (chprot_release_time * getSampleRate()) / 1000;

chprot_current_envelope = 1.0f;
chprot_current_env_period = 0;
post_last_sample = 0.0f;
post_demerit = 0.0f;
chprot_windowopen = 0;
chprot_windowaclose = 0;


To reset:

chprot_current_envelope = 1.0f;
chprot_current_env_period = 0;
post_last_sample = 0.0f;
post_demerit = 0.0f;

Work:
if (overload_enableburst == 1) {
    bufrel = (float)(32767.0f / (float)chprot_release_samples) / 32767.0f;
    nmsp2 = numsamples * 2;
    for (i = 0; i < nmsp2; ++ i) {
        if (post_demerit > 0) post_demerit--;
        if (psamples[i] > chprot_peak_threshold) post_demerit+=3;
        if (fabs(post_last_sample - psamples[i]) > chprot_delta_threshold) post_demerit+=3;
        if (post_demerit > 8000) {
            chprot_current_envelope = 0.01f;
            chprot_current_env_period = 0;
        }
        if (chprot_current_envelope < 1.0f) {
            chprot_current_env_period++;
            if (chprot_current_env_period > chprot_silence_samples) {
                chprot_current_envelope += bufrel;
                if (chprot_current_envelope > 0.70f) {
                    chprot_windowaclose = 0;
                }
            }
        } else if (chprot_current_envelope > 1.0f) {
            chprot_current_envelope = 1.0f;
            chprot_windowaclose = 0;
        } else {
            chprot_windowaclose = 0;
        }

        psamples[i] *= chprot_current_envelope;
        post_last_sample = psamples[i];
        ++ i;
        psamples[i] *= chprot_current_envelope;
    }
}