supersonic написал(а):
Это связано с тем, что Ку/Ню искусственно добавляет шум в 32-ой бит. Сделано это для борьбы с возможной денормализацией - об этом программисты Стайнберга где-то на своем форуме писали.
Набрел на занятный плагинчик
http://cjcity.ru/soft/117-14.html по этой теме
Вот к нему описалово:
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normalizer
denormals eleminator VST plugin
written by Sascha Eversmeier
www.digitalfishphones.com
Mac version compiled by Urs Heckmann (
www.u-he.com)
readme file
date: 2002/08/06
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plugin file: 'normalizer' (send / insert plugin)
This plugin does nothing fancy except just injecting some noise into the plugin chain.
You might need some additional noise if you encounter CPU spikes or serious performance problems whenever there is no incoming audio feeding an active plugin.
This may occur with certain plugins that don't come with proper methods to cancel the so-called 'denormals'.
This is an issue with some audio hosts that don't switch off the plugin's audio path when the song is stopped. Additionally, denormalistaion can also occur whenever a track contains pure silence.
Denormalisation happens when the CPU (precisely: the FPU inside of it) detects extremely small numbers and wishes to process them with the same precision as usual.
Some algorithm such as delay lines and filters are prone to denormalisation as they work with feedback structures.
Here, if an impulse is followed by absolute silence, the resulting signal gets smaller and smaller but in theory, it can never reach zero. In practice,
there is an internal threshold of the FPU that switches to denormal mode to carry on processing those small numbers (which might not be of any use for proper operation).
Currently, the Pentium 4 processor seems highly addicted to denormalisation. It seems that its threshold is actually very much higher than of former Pentium types.
Sadly, this eats up most of the available processing power and should be avoided under any circumstances.
Plugins that used to work fine with older CPUs might slow down the entire system when used with a P4.
But there are even problems with some plugins under the MacOS. Any FPU using both normalised and denormalised operands can cause such troubles.
Most developers are aware of the problem though the methods to avoid it are many. Some algorithms ask for the current FPU status from time to time, reacting to it by changing small values to zero.
Other developers prefer adding an an extra signal to the audio which is carried along the entire process of the plugin, thereby forcing it to remain above the internal threshold.
Should the input become silent, the additional noise will still keep the whole thing from denormalizing. All the digitalfishphones plugins actually work this way, and so does the Normalizer.
Normalizer usage:
Fill the first insert or fx slot with this plugin. Put the plugin causing denormalisation into the second slot.
The normalizer plugin lets you choose between two methods: adding AC or DC signal.
Here, AC is a square wave ringing at the nyquist frequency (half the sampling rate, e.g. 22.05kHz).
Choose this method whenever the following plugin does not apply intensive low-pass filtering, thereby eleminating our injection noise.
In that case, the DC method could be used. It just adds a static offset to the signal. This DC level (when set pretty low) should be no issue with further processing of the resulting output.
No matter which method you choose from, the noise floor should be lower than the lowest value that a modern D/A converter can handle.
And in fact, a level of about -300 to -200dB is usually enough. At times, you can even go much lower.
You will have to experiment with the proper level because the internal working of the faulty plugin is unknown to us.
The more stages it involves, the more complex the whole thing is.
Happy normalizing
Sascha Eversmeier
http://www.digitalfishphones.com
sascha@digitalfishphones.com
MacOS version compiled by Urs Heckmann. Check his stuff at
http://www.u-he.com
ioneer_smoke:
