On 2015-07-09 18:55, Paul B Mahol wrote: > diff --git a/doc/filters.texi b/doc/filters.texi > index 3fce874..74c408a 100644 > --- a/doc/filters.texi > +++ b/doc/filters.texi > @@ -1520,6 +1520,164 @@ Optional. It should have a value much less than 1 > (e.g. 0.05 or 0.02) and is > used to prevent clipping. > @end table > > +@section dynaudnorm > +Dynamic Audio Normalizer. > + > +This filter applies a certain amount of gain to the input audion in order ^^^^^^ "audio"
> +to bring its peak magnitude to a target level (e.g. 0 dBFS). However, in > +contrast to more "simple" normalization algorithms, the Dynamic Audio > +Normalizer *dynamically* re-adjusts the gain factor to the input audio. > +This allows for applying extra gain to the "quiet" sections of the audio > +while avoiding distortions or clipping the "loud" sections. In other words: > +The Dynamic Audio Normalizer will "even out" the volume of quiet and loud > +sections, in the sense that the volume of each section is brought to the > +same target level. Note, however, that the Dynamic Audio Normalizer achieves > +this goal *without* applying "dynamic range compressing". It will retain 100% > +of the dynamic range *within* each section of the audio file. > + > +@table @option > +@item f > +Set the frame length in milliseconds. In range from 10 to 8000 milliseconds. > +Default is 500 milliseconds. > +The Dynamic Audio Normalizer processes the input audio in small chunks, > +referred to as frames. This is required, because a peak magnitude has no > +meaning for just a single sample value. Instead, we need to determine the > +peak magnitude for a contiguous sequence of sample values. While a "standard" > +normalizer would simply use the peak magnitude of the complete file, the > +Dynamic Audio Normalizer determines the peak magnitude individually for each > +frame. The length of a frame is specified in milliseconds. By default, the > +Dynamic Audio Normalizer uses a frame length of 500 milliseconds, which has > +been found to give good results with most files. > +Note that the exact frame length, in number of samples, will be determined > +automatically, based on the sampling rate of the individual input audio file. > + > +@item g > +Set the Gaussian filter window size. In range from 3 to 301, must be odd > +number. Default is 31. > +Probably the most important parameter of the Dynamic Audio Normalizer is the > +@code{window size} of the Gaussian smoothing filter. The filter's window size > +is specified in frames, centered around the current frame. For the sake of > +simplicity, this must be an odd number. Consequently, the default value of 31 > +takes into account the current frame, as well as the 15 preceding frames and > +the 15 subsequent frames. Using a larger window results in a stronger > +smoothing effect and thus in less gain variation, i.e. slower gain > +adaptation. Conversely, using a smaller window results in a weaker smoothing > +effect and thus in more gain variation, i.e. faster gain adaptation. > +In other words, the more you increase this value, the more the Dynamic Audio > +Normalizer will behave like a "traditional" normalization filter. On the > +contrary, the more you decrease this value, the more the Dynamic Audio > +Normalizer will behave like a dynamic range compressor. > + > +@item p > +Set the target peak value. This specifies the highest permissible magnitude > +level for the normalized audio input. This filter will try to approach the > +target peak magnitude as closely as possible, but at the same time it also > +makes sure that the normalized signal will never exceed the peak magnitude. > +A frame's maximum local gain factor is imposed directly by the target peak > +magnitude. The default value is 0.95 and thus leaves a headroom of 5%*. > +It is not recommended to go above this value. > + > +@item m > +Set the maximum gain factor. In range from 1.0 to 100.0. Default is 10.0. > +The Dynamic Audio Normalizer determines the maximum possible (local) gain > +factor for each input frame, i.e. the maximum gain factor that does not > +result in clipping or distortion. The maximum gain factor is determined by > +the frame's highest magnitude sample. However, the Dynamic Audio Normalizer > +additionally bounds the frame's maximum gain factor by a predetermined > +(global) maximum gain factor. This is done in order to avoid excessive gain > +factors in "silent" or almost silent frames. By default, the maximum gain > +factor is 10.0, For most inputs the default value should be sufficient and > +it usually is not recommended to increase this value. Though, for input > +with an extremely low overall volume level, it may be necessary to allow even > +higher gain factors. Note, however, that the Dynamic Audio Normalizer does > +not simply apply a "hard" threshold (i.e. cut off values above the > threshold). > +Instead, a "sigmoid" threshold function will be applied. This way, the > +gainfactors will smoothly approach the threshold value, but never exceed that ^^^^^^^^^^^ "gain factors", maybe. P.S. Sorry about the two messages.
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