StArSeEd
July 1st 03, 07:59 PM
Per Stromgren:
> (Posted earlier in rec.audio.tech with no protests, I take that as an
> agreement of sorts.)
> The threads that are hovering around Mykes work with sound files are
> very much a discussion of what the words mean. In order to put that
> particular discussion to rest I invite the parties to come to an
> agreement about the words. I propose the following descriptions of
> these often discussed words:
> *** Normalize - to scale an entire sound file in order for its loudest
> sample to hit full scale (0db FS), or a tiny bit less. This is
> performed by first looking up the loudest sample, and then multiply
> all samples by the (constant) factor that takes the loudest up to a
> fraction under 0dB FS. The sound file's average level is not taken
> into account at all when calculating the gain, only its loudest
> sample. The effect is like turing the wolume knob up.
You might want to differentiate between Peak Normalization and RMS
Normalization (as a Peak Normalization definition, yours is almost
perfect).
Peak Normalization: scaling the amplitudes of all frequencies in a
sound file such that the highest peak is of a chosen amplitude. Never
introduces clipping, except in the case of a previous hard limiting.
Increases both dynamic range and S/N ratio.
RMS Normalization: scaling the amplitudes of all frequencies in a
sound file such that the RMS (Root Mean Square) average (apparent
volume; usually takes into account an equal loudness contour during
initial RMS calculation) is of a chosen volume. Can clip unless
measures are taken to prevent this (limiting or compression).
Usually used to match apparent volume levels between two or more
sound files.
> *** Clipping - what often happens to a signal that is too loud for a
> system. An amplifier can't put out more than plus and minus rail
> voltage; any signal louder than that is "clipped" to this voltage,
> which sounds awful. The same thing happens when you hit 0dB FS in a
> digital system; it can't put out more than "all bits on" (not always
> to be taken literally). This maximum level is sometimes called clip
> level.
I would add "for two or more consecutive samples" after "hit 0dB FS"
and a note that it sounds like total ass when audio clips. A note about
wrapping might also be in order.
> *** Limiting - what you perhaps want to do to a signal in order for it
> to fit under your systems clip level, but not being clipped. It can be
> accomplished by adjusting the gain for the signal, when it is to reach
> clip level. This can be done by hand or automatically. In any case you
> will get a compression of the signal.
Hard limiting: forced 'clipping' at a level lower than 0dB FS.
Straight-line peak trim. Can sound very harsh.
Soft limiting: compression applied only to the highest peaks to prevent
clipping, usually before a normalization; "shallow" compression.
> *** Compression - A non-linear transpose function where the gain is a
> function of the signal level. Most often it is used to amplify soft
> passages more than loud ones to avoid the soft ones to drown in noise,
> but is also used as an effect in modern music. Compressing is also
> used as part of other signal handling, Dolby NR for instance. The
> effect of compression on music is that it sounds louder, because its
> average level has gone up.
Looks good, but a note about decreasing dynamic range wouldn't hurt.
Might also want to add its opposite, Expanding, to the list.
Is there a process which simply ADDS a chosen value to each and every
positive sample and subtracts that value from each and every negative
sample (ie, not DC offset - I want to shift equally in both directions)?
And yes, I realize this would raise the noise floor considerably...
-StArSeEd
--
dchub://tsphub.dyndns.org:1979
IRC EFnet #smashing_pumpkins
Email:
ICQ UIN: 1711589
> (Posted earlier in rec.audio.tech with no protests, I take that as an
> agreement of sorts.)
> The threads that are hovering around Mykes work with sound files are
> very much a discussion of what the words mean. In order to put that
> particular discussion to rest I invite the parties to come to an
> agreement about the words. I propose the following descriptions of
> these often discussed words:
> *** Normalize - to scale an entire sound file in order for its loudest
> sample to hit full scale (0db FS), or a tiny bit less. This is
> performed by first looking up the loudest sample, and then multiply
> all samples by the (constant) factor that takes the loudest up to a
> fraction under 0dB FS. The sound file's average level is not taken
> into account at all when calculating the gain, only its loudest
> sample. The effect is like turing the wolume knob up.
You might want to differentiate between Peak Normalization and RMS
Normalization (as a Peak Normalization definition, yours is almost
perfect).
Peak Normalization: scaling the amplitudes of all frequencies in a
sound file such that the highest peak is of a chosen amplitude. Never
introduces clipping, except in the case of a previous hard limiting.
Increases both dynamic range and S/N ratio.
RMS Normalization: scaling the amplitudes of all frequencies in a
sound file such that the RMS (Root Mean Square) average (apparent
volume; usually takes into account an equal loudness contour during
initial RMS calculation) is of a chosen volume. Can clip unless
measures are taken to prevent this (limiting or compression).
Usually used to match apparent volume levels between two or more
sound files.
> *** Clipping - what often happens to a signal that is too loud for a
> system. An amplifier can't put out more than plus and minus rail
> voltage; any signal louder than that is "clipped" to this voltage,
> which sounds awful. The same thing happens when you hit 0dB FS in a
> digital system; it can't put out more than "all bits on" (not always
> to be taken literally). This maximum level is sometimes called clip
> level.
I would add "for two or more consecutive samples" after "hit 0dB FS"
and a note that it sounds like total ass when audio clips. A note about
wrapping might also be in order.
> *** Limiting - what you perhaps want to do to a signal in order for it
> to fit under your systems clip level, but not being clipped. It can be
> accomplished by adjusting the gain for the signal, when it is to reach
> clip level. This can be done by hand or automatically. In any case you
> will get a compression of the signal.
Hard limiting: forced 'clipping' at a level lower than 0dB FS.
Straight-line peak trim. Can sound very harsh.
Soft limiting: compression applied only to the highest peaks to prevent
clipping, usually before a normalization; "shallow" compression.
> *** Compression - A non-linear transpose function where the gain is a
> function of the signal level. Most often it is used to amplify soft
> passages more than loud ones to avoid the soft ones to drown in noise,
> but is also used as an effect in modern music. Compressing is also
> used as part of other signal handling, Dolby NR for instance. The
> effect of compression on music is that it sounds louder, because its
> average level has gone up.
Looks good, but a note about decreasing dynamic range wouldn't hurt.
Might also want to add its opposite, Expanding, to the list.
Is there a process which simply ADDS a chosen value to each and every
positive sample and subtracts that value from each and every negative
sample (ie, not DC offset - I want to shift equally in both directions)?
And yes, I realize this would raise the noise floor considerably...
-StArSeEd
--
dchub://tsphub.dyndns.org:1979
IRC EFnet #smashing_pumpkins
Email:
ICQ UIN: 1711589