Reply by Richard Owlett●December 15, 20052005-12-15
Jerry Avins wrote:
> Richard Owlet wrote:
>
>> Jon Harris wrote:
>>
>>> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message
>>> news:ICEmf.35582$Zv5.15048@newssvr25.news.prodigy.net...
>>>
>>>>
>>>> Jerry Avins wrote:
>>>>
>>>>
>>>>> I wish car radios had compressors so I could ride over road noise
>>>>> with open windows without blasting myself on louder passages. It's
>>>>> not a great way to listen to music, but it's better than not
>>>>> listening.
>>>>
>>>>
>>>>
>>>> ...The FM broadcast is usually heavily compressed too.
>>>
>>>
>>>
>>>
>>> Almost always true for pop music stations, but much less so for
>>> classical stations.
>>>
>>
>> I once was a studio engineer for a student operated full commercial
>> license FM station that was a member of the QXR network
>> (rebroadcasting WQXR out of NYC).
>>
>> You would have been drawn, quartered, salted, boiled in oil and *THEN*
>> tortured for even thinking compressors etc ;!
>
>
> Not at the transmitter, but in the (car) receiver. Or did you miss that?
>
> Jerry
yes
Reply by Jon Harris●December 14, 20052005-12-14
"Richard Owlett" <rowlett@atlascomm.net> wrote in message
news:11pucfacghtsa88@corp.supernews.com...
> Jon Harris wrote:
>
>> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message
>> news:ICEmf.35582$Zv5.15048@newssvr25.news.prodigy.net...
>>
>>>
>>>Jerry Avins wrote:
>>>
>>>
>>>>I wish car radios had compressors so I could ride over road noise with open
>>>>windows without blasting myself on louder passages. It's not a great way to
>>>>listen to music, but it's better than not listening.
>>>
>>>...The FM broadcast is usually heavily compressed too.
>>
>>
>> Almost always true for pop music stations, but much less so for classical
>> stations.
>
> I once was a studio engineer for a student operated full commercial license FM
> station that was a member of the QXR network (rebroadcasting WQXR out of NYC).
>
> You would have been drawn, quartered, salted, boiled in oil and *THEN*
> tortured for even thinking compressors etc ;!
OK, but since you were just re-broadcasting other content, it would presumably
already have been squeezed where it originated.
Nowadays, many stations use a "broadcast processor", which is basically a
multi-band (like 5) compressor, plus other bells and whistles to squeeze the
heck out of the audio. Examples can be found at http://www.orban.com/ and
http://www.omniaaudio.com/.
Reply by Jerry Avins●December 13, 20052005-12-13
Richard Owlet wrote:
> Jon Harris wrote:
>
>> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message
>> news:ICEmf.35582$Zv5.15048@newssvr25.news.prodigy.net...
>>
>>>
>>> Jerry Avins wrote:
>>>
>>>
>>>> I wish car radios had compressors so I could ride over road noise
>>>> with open windows without blasting myself on louder passages. It's
>>>> not a great way to listen to music, but it's better than not listening.
>>>
>>>
>>> ...The FM broadcast is usually heavily compressed too.
>>
>>
>>
>> Almost always true for pop music stations, but much less so for
>> classical stations.
>>
>
> I once was a studio engineer for a student operated full commercial
> license FM station that was a member of the QXR network (rebroadcasting
> WQXR out of NYC).
>
> You would have been drawn, quartered, salted, boiled in oil and *THEN*
> tortured for even thinking compressors etc ;!
Not at the transmitter, but in the (car) receiver. Or did you miss that?
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Richard Owlett●December 13, 20052005-12-13
Jon Harris wrote:
> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message
> news:ICEmf.35582$Zv5.15048@newssvr25.news.prodigy.net...
>
>>
>>Jerry Avins wrote:
>>
>>
>>>I wish car radios had compressors so I could ride over road noise with open
>>>windows without blasting myself on louder passages. It's not a great way to
>>>listen to music, but it's better than not listening.
>>
>>...The FM broadcast is usually heavily compressed too.
>
>
> Almost always true for pop music stations, but much less so for classical
> stations.
>
>
I once was a studio engineer for a student operated full commercial
license FM station that was a member of the QXR network (rebroadcasting
WQXR out of NYC).
You would have been drawn, quartered, salted, boiled in oil and *THEN*
tortured for even thinking compressors etc ;!
Reply by Jon Harris●December 13, 20052005-12-13
<robert.w.adams@verizon.net> wrote in message
news:1134264573.722591.286330@g47g2000cwa.googlegroups.com...
>I have done lots of digital compressors. RMS detection is a good way to
> go because of the following;
>
> RMS detectors have strange transient behavior because they look like a
> 1st-order lowpass filter fed by the square of the input signal. That
> means the attack time-constant is dependant on the size of the
> amplitude step you are making, since it gets squared before being
> applied to the filter. But there is a workable compromise for the time
> constant that is fast enough for most normal applications, without
> causing too much distortion on steady sine-waves (RMS detectors produce
> a ripple on their outputs at 2X the input frequency, causing
> 3rd-harmonic distortion).
Bob, would you mind elaborating on that a bit, i.e. the time constant compromise
stuff?
Reply by Jon Harris●December 13, 20052005-12-13
"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message
news:ICEmf.35582$Zv5.15048@newssvr25.news.prodigy.net...
>
>
> Jerry Avins wrote:
>
>> I wish car radios had compressors so I could ride over road noise with open
>> windows without blasting myself on louder passages. It's not a great way to
>> listen to music, but it's better than not listening.
>
> ...The FM broadcast is usually heavily compressed too.
Almost always true for pop music stations, but much less so for classical
stations.
Reply by Martin Eisenberg●December 11, 20052005-12-11
__GG wrote:
> On Fri, 09 Dec 2005 21:52:25 GMT, Richard Dobson
> <richarddobson@blueyonder.co.uk> wrote:
>
>>http://www.musicdsp.org/archive.php?classid=4#204
>
> Thanks again for the reference, Richard. I've looked through
> that code and realized that I'm missing something. For one, the
> DC_OFFSET that's added in "to avoid log(0)."
The logarithm has a pole at zero, corresponding to -infinity dB. So
the code clamps the gain to some small value.
> Another... I don't see where AttRelEnvelope is used.
Right, the main class duplicates the functionality.
Martin
--
Quidquid latine scriptum sit, altum viditur.
Reply by Jerry Avins●December 11, 20052005-12-11
Richard Dobson wrote:
> Jerry Avins wrote:
> ..
>
>> Richard,
>>
>> The simplest way I came up with to make a well behaved compressor with
>> variable compression was to use a very flat compressor (1 dB variation
>> of output level for 10 dB variation of input) output to one end of a
>> fader pot and the uncompressed signal to the other end. Setting the
>> slider chose the compression amount. Is your new product easily variable?
>>
>> Jerry
>
>
> Not exactly in the way you describe. My design is entirely orthodox in
> that there is a user-variable threshold above which the compression
> applies, together with a variable compression slope. Your ratio of 10 is
> moderately steep (getting towards acting as a limiter). The only other
> standard refinement is to offer a choice of "hard" or "soft" knee, which
> simply says the transition between uncompressed and compressed is not
> represented by two lines at an angle, but by a nice rounded curve at the
> transition point. Just how rounded that curve might be is where the most
> individuality in a compressor can come in - in the limit it can make the
> whole transfer function a curve, rather than two straight lines with a
> rounded corner. The "simple" code examples one sees of compressors all
> use a 100% hard knee, as the code simply says "if above this value, do
> that". A soft knee requires a more elaborate approach - several ways to
> do it, needless to say, including the use of a literal stored transfer
> function. Quite a few commercial examples offer a custom user interface
> where you can see the transfer function drawn graphically, and even with
> control points to set parameters graphically with the mouse**.
>
> It is not usual in a compressor to offer a wet/dry mix control, which
> is what you describe, (depends in any case on the lookahead delay
> compensation being accurate, and unfortunately one cannot always rely on
> hosts doing that).
>
>
> ** One example of this is the "Cakewalk FX Compressor/Gate", supplied
> with SONAR, whrere indeed you have control of two turning points withkn
> the one effect.
My cobbled-together version was a variation of Mercury's microphone
compressor, but only half as good. With fast attack and modestly long
release, it was good with voice and acceptable for music. I'm sure there
are lots of ways to vary the compression with a knob. The one I used
seemed simple, so I did it. Although the compressor uses voltage
dividers with diodes as one of the elements, distortion never exceeded
.2% THD when I tested it at various levels. The design inherently has a
long tail to the decay which can be mitigated with a shunt resistor.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Richard Dobson●December 11, 20052005-12-11
robert.w.adams@verizon.net wrote:
> I have done lots of digital compressors. RMS detection is a good way to
> go because of the following;
>
> When you play a musical note on an instrument like a piano, the
> harmonics are NOT pure multiples of the fundamental. So if you look at
> the waveform on a scope, after the initial attack you will see parts of
> the waveform that have large peaks (because the instantaneous phase of
> the harmonics is aligned in a certain way) and others where the
> peak-to-average ratio is quite small. ..
There are two distinct applications of a compressor. The first is what one might
call macro-compression, perhaps applied to a whole vocal phrase. The goal here
is to keep the overall loudness down, without (hopefully)otherwise colouring the
sound. The likely confuration would be an RMS detector, with a medium to long
attack and release times (could be as much as 300msecs). This is for example the
job of an analog conditioning chain, to tame exuberant vocals before they are
digitised.
A second application is peak transient reduction, most especially in drums,
which can generate extreme peaks which force the overlal level down to avoid
clipping. The goal here is lodness maximisation, by compressing the peaks so
that the overall level can be raised. Here a PEAK detector (typically combined
with lookahead) can work extremely well, to compress a peak that may only last a
few msecs. In other words, used this way the compressor effectively changes the
envelope of a single sound; both attack and release times may be just a few
msecs. Inevitably, the sound may be more coloured, but with drums that seems
less important than regaining all that lost headroom. Of course, one can
compromise by doing RMS detection over a very short window (say, 5msecs or even
less), and I suspect some "Peak" options in compressors actually do it this way.
I did find however that a plain peak detector, combined with a soft-ish knee,
works pretty well on drums. But on something like a piano, using this form of
compression is likely to change the character of the sound, by changing its
envelope. On drums, the timbre change between the hit and the tail is important,
so you can get away with heavy comression (which is of course a desired sound in
it own right these days) while for a piano the envelope itself is also
important; you run the risk of turning an acoustic piano into an electronic one!
Or, described yet another way, short-window or peak compression is suited to the
processing of a single (monophonic) voice, whereas macro-RMS compression may be
applied to a whole (polyphonic) mix.
Imagine the problems in compressing a polyphonic piano track, where a first note
or chord is sustained, while a second note is struck. If you set the compressor
fast enough to modify the envelope of the second note, that modification will be
applied to the sustained note too!
Richard Dobson
Reply by Richard Dobson●December 11, 20052005-12-11
Jerry Avins wrote:
..
> Richard,
>
> The simplest way I came up with to make a well behaved compressor with
> variable compression was to use a very flat compressor (1 dB variation
> of output level for 10 dB variation of input) output to one end of a
> fader pot and the uncompressed signal to the other end. Setting the
> slider chose the compression amount. Is your new product easily variable?
>
> Jerry
Not exactly in the way you describe. My design is entirely orthodox in that
there is a user-variable threshold above which the compression applies, together
with a variable compression slope. Your ratio of 10 is moderately steep (getting
towards acting as a limiter). The only other standard refinement is to offer a
choice of "hard" or "soft" knee, which simply says the transition between
uncompressed and compressed is not represented by two lines at an angle, but by
a nice rounded curve at the transition point. Just how rounded that curve might
be is where the most individuality in a compressor can come in - in the limit it
can make the whole transfer function a curve, rather than two straight lines
with a rounded corner. The "simple" code examples one sees of compressors all
use a 100% hard knee, as the code simply says "if above this value, do that". A
soft knee requires a more elaborate approach - several ways to do it, needless
to say, including the use of a literal stored transfer function. Quite a few
commercial examples offer a custom user interface where you can see the transfer
function drawn graphically, and even with control points to set parameters
graphically with the mouse**.
It is not usual in a compressor to offer a wet/dry mix control, which is what
you describe, (depends in any case on the lookahead delay compensation being
accurate, and unfortunately one cannot always rely on hosts doing that).
** One example of this is the "Cakewalk FX Compressor/Gate", supplied with
SONAR, whrere indeed you have control of two turning points withkn the one effect.
Richard Dobson