[bct] How limiters and compressers work when recording

  • From: "Neal Ewers" <neal.ewers@xxxxxxxxxxxxxx>
  • To: <blindcooltech@xxxxxxxxxxxxx>
  • Date: Mon, 6 Mar 2006 10:21:48 -0600

Mike and list, I changed the subject from Recording on the Olympus
because this message turned into a rather long message to answer a
question.  Don't take what I am about to say as a criticism of Larry's
podcasts or anyone else's podcasts who use this recorder.  This is
simply an attempt to answer a technical question you raise.

I believe what you were hearing was the recorder's limiter being
overworked.  Unfortunately, these recorders do not have a record level
you can set and then have the limiter kick in to level off the more
noisy sounds.  If they did, you might set the volume a bit higher than
you would if you did not have a limiter.  This would cause the limiter
to work, but only a bit.  The higher you set the record level above
where it would distort if you didn't have a limiter, the more limiting
you hear.  The Olympus recorders have set a stationary volume level that
is quite high, and thus you hear the limiter working.  Larry, one
question, are you recording in conference or dictate mode when you make
these podcasts?  To further the explanation, conference mode will set
the volume higher with the idea that you are wanting to record far away
sounds.  The dictation mode will set the volume lower, but as the mikes
Larry often uses are quite high in volume to begin with, using dictation
mode may solve some of the problem.

There is no limiter on the Microtrack recorder, thus, when Larry records
his walks home on this, he has to set the volume quite low to keep from
being distorted.  Thus, there is a greater dynamic range to his
podcasts.  The loud sounds are quite loud and the soft sounds are much
lower.  So, having a limiter compress some of the audio does make it
easier to listen to, because you don't have to constantly adjust your
hearing from really loud sounds to really soft sounds.  And, you always
have the fear that you didn't set the volume on the recorder low enough
and a large truck will go by and distort the sound.  So, you set the
level even lower to keep this from happening.  Unfortunately, the noise
floor of the Microtrack, or the noise it puts into the recording when no
signal is present, is quite high.  Thus, the lower you turn the volume,
the more likely you are going to hear the inherent noise of the recorder
which is rather like a hissing sound.  Of course, if there is a lot of
signal, like traffic, you don't hear the noise of the recorder because
the signal recorded is loud enough to mask out that noise.

One way to solve this problem, if you have the equipment to do so, is to
record at 48 Sampling rate and a bit rate of 24.  Now, the noise floor
of the recording is much more quiet, so you can turn the volume down to
insure that you do not distort the sounds around you.  You then use the
limiter capability of some kind of software editor like Gold Wave or
Sound forge.  Now you have the opportunity to adjust the amount of the
compression, listen to the sound, and determine if you are hearing too
little or too much compression.  And this brings me to the discussion of
limiting versus compression.

A limiter simply takes the loud sounds off of the top, while a
compressor will not only do this, but it will bring the low sounds in
the recording to a higher volume as well.  Take, for example, what
happens in Sound forge.  You can set the limiter threshold to, for
example, limit the higher sounds by 6 DB.  If you do nothing else, then
what you have is a true limiter.  However, you can also say to Sound
Forge, OK, you have lowered the high sounds by 6 DB, now let's raise the
overall volume of the recording by that same 6 DB.  Now, what you have
is a sound that is both limited and compressed.  The higher volume
sounds do not sound as loud, but since you have raised the overall
volume, the softer sounds are now not as soft.

Well, I didn't know this was going to turn into a long explanation of
this subject, but I guess my fingers wanted something to do besides
prepare dinner for my lovely wife.  So, there you have it.


Neal


-----Original Message-----
From: blindcooltech-bounce@xxxxxxxxxxxxx
[mailto:blindcooltech-bounce@xxxxxxxxxxxxx] On Behalf Of Mike
Sent: Sunday, March 05, 2006 11:03 PM
To: blindcooltech@xxxxxxxxxxxxx
Subject: [bct] Re: Recordings on the Olympus ws320M


I listened to the Atia recordings Larry. It was a noisy exhibit hall you
were in. For some reason the voices that were background while you
conversed with different people pumped a bit. You or the other person
would speak and knock the crowd noise down a little and then the
background would come up between your pauses. It reminded me of
listening to encoded noise reduction without the decoding a little. It
was all plenty intelligible. The quality, the fidelity, if you will, was
good, but I wondered if what I was hearing was a function of the
compression rate in the first place or the conversions to and from wave
files and back or whether the recorder was the culprit. Now in another
pod cast, the meeting with the Library of Congress at the NFB
convention, the speakers were not amplified and they were at some
distance from you, but the room sound was very natural. I mean we were
sitting right there with you man.



-----Original Message-----
From: blindcooltech-bounce@xxxxxxxxxxxxx
[mailto:blindcooltech-bounce@xxxxxxxxxxxxx]On Behalf Of Larry Skutchan
Sent: Sunday, March 05, 2006 8:24 PM
To: blindcooltech@xxxxxxxxxxxxx
Subject: [bct] Re: Recordings on the Olympus ws320M


Well, let me put it this way.  That ws-320M and a set of binourals are
always on me.  I used tthe Olympus at ATIA, and I will use it at CSUN,
too. For that kind of environment, you can't beat it.  For a sound
seeing tour, I'd probably go with the Iriver.
----- Original Message -----
From: "Jeff Bishop" <jeff.bishop@xxxxxxxxx>
To: <blindcooltech@xxxxxxxxxxxxx>
Sent: Sunday, March 05, 2006 6:42 PM
Subject: [bct] Re: Recordings on the Olympus ws320M


> Larry,
>
> If it were you, what would you use between the two, the Iriver?  My 
> fear is that the Iriver may not record, I have had this happen in the 
> past.
>
> -----Original Message-----
> From: blindcooltech-bounce@xxxxxxxxxxxxx
> [mailto:blindcooltech-bounce@xxxxxxxxxxxxx] On Behalf Of Larry 
> Skutchan
> Sent: Sunday, March 05, 2006 3:16 PM
> To: blindcooltech@xxxxxxxxxxxxx
> Subject: [bct] Re: Recordings on the Olympus ws320M
>
> The one really good thing about the Olympus is that it does have 
> automatic gain control and limiting, so it is possible to get some 
> really good recordings, but that diff between 64 and 96 really makes a

> difference. Plus, you never have to worry about clipping and levers.
> ----- Original Message -----
> From: "Jeff Bishop" <jeff.bishop@xxxxxxxxx>
> To: <blindcooltech@xxxxxxxxxxxxx>
> Sent: Sunday, March 05, 2006 3:37 PM
> Subject: [bct] Re: Recordings on the Olympus ws320M
>
>
>> Is it simply a bit difference from 96 to 64 and is it that noticable 
>> of a difference?  For example, does the Olympus provide better 
>> recordings in a conference type mode (where you are quite a bit away 
>> from the speaker for example).
>>
>> Jeff
>>
>>
>> -----Original Message-----
>> From: blindcooltech-bounce@xxxxxxxxxxxxx
>> [mailto:blindcooltech-bounce@xxxxxxxxxxxxx] On Behalf Of Larry 
>> Skutchan
>> Sent: Sunday, March 05, 2006 1:11 PM
>> To: blindcooltech@xxxxxxxxxxxxx
>> Subject: [bct] Re: Recordings on the Olympus ws320M
>>
>> No way Jeeff.  That Iriver gives a much better recording, but the 
>> Olympus is easier to use and does a desceent job.
>>
>> The 320M supports protected WMA, according to its manual, but I have 
>> not been able to make this work.
>> ----- Original Message -----
>> From: "Jeff Bishop" <jeff.bishop@xxxxxxxxx>
>> To: <blindcooltech@xxxxxxxxxxxxx>
>> Sent: Sunday, March 05, 2006 2:15 PM
>> Subject: [bct] Recordings on the Olympus ws320M
>>
>>
>>> Hello Everyone,
>>>
>>> I seem to recall some podcasts from Larry about issues with 
>>> recordings on the Olympus 320M.  Can anyone advise as to this?  I am

>>> looking at buying one for my trip to CSUN as I think it will provide

>>> better quality then my IFP899
>>> Iriver.  What do you think?
>>>
>>> What bit rate does the 320M support?
>>>
>>> Has anyone gotten Overdrive or Net Library (protected wma) files to 
>>> work with the 320M?
>>>
>>> Jeff Bishop
>>>
>>>
>>
>>
>>
>
>
>






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  • » [bct] How limiters and compressers work when recording