A question for audio engineers

[ggw]

Originally posted by Ellis D. Fleischbach:
   

Originally posted by beetsnotbeats:
  The Volume Logic plugin works pretty well at evenning out playback levels from software players (iTunes, Musicmatch, Winamp, etc.), and it's cheaper than a new piece of hardware. But you gotta hook yr computer up to yr stereo, which should be pretty easy.

That looks like reasonable software, but what I would also like is a user-friendly component that will fix CD multidisc randoming, as well. [/b]

http://www.research-lab.com/avcdsp.htm

[thetallerpaul]

i just burn cds and normalize them

[chaz]

I'd be happy with a new ipod dock that has some sort of digital audio out.

[valkenswaard]

Ellis,
 
 What you are describing is called Automatic Gain Control (AGC).  Symetrix Audio makes a single-space rackmount unit called the 422, which is popular with both broadcasters and audiophiles.  It's a stereo unit that accepts line level audio inputs.  Retail is $549 and they usually sell for a little over $400 new.
 
 Here's a link to more info on the unit:
   http://www.symetrixaudio.com/index.php?Show=14&Show1=&Show2=260  
 
 I hope this helps.  Let me know if you have any questions.
 
 Jerry
 
 Sorry, I removed the other link.  I didn't want the moderators to think I was spamming.

Originally posted by valkenswaard:
  Ellis,
 
 What you are describing is called Automatic Gain Control (AGC).  Symetrix Audio makes a single-space rackmount unit called the 422, which is popular with both broadcasters and audiophiles.  It's a stereo unit that accepts line level audio inputs.  Retail is $549 and they usually sell for a little over $400 new.
 
 Here's a link to more info on the unit:
    http://www.symetrixaudio.com/index.php?Show=14&Show1=&Show2=260  
 
 I hope this helps.  Let me know if you have any questions.
 
 Jerry
 
 Sorry, I removed the other link.  I didn't want the moderators to think I was spamming.

I bookmarked it.  I'll definitely give that a good eyeballing.  Thanks!  Gold star 4U.

[Sir HC]

Those are the same things that they use in doctors offices and other places.  There is a lag in volume as it takes quite a while to determine it should come up or down.  Can be annoying and I didn't see a time control on the front.  Still that would do what you want very well.

What does it mean, volume lag?

[Sir HC]

Imagine that when it is too quiet, it will take say 5 seconds to come up to volume and visa versa.  Since the change in volume of the material drives its automatic gain control (AGC), it can not work until the change on the input side has happened.  To keep the dynamics of the music from causing it to "pump" (where it sounds like someone turning the volume knob to the beat), it has a long delay on the volume control.  If you look at compressors (a similar item) there often are controls for attack and decay which sets how long it takes for the compressing action to take place.  The manual for this doesn't mention the numbers for this device, but I would have to guess a few seconds otherwise it could get false readings from drums or the like.

Well that's a red check mark, then.

[pip]

Originally posted by Sir HC:
  Imagine that when it is too quiet, it will take say 5 seconds to come up to volume and visa versa.  Since the change in volume of the material drives its automatic gain control (AGC), it can not work until the change on the input side has happened.  To keep the dynamics of the music from causing it to "pump" (where it sounds like someone turning the volume knob to the beat), it has a long delay on the volume control.  If you look at compressors (a similar item) there often are controls for attack and decay which sets how long it takes for the compressing action to take place.  The manual for this doesn't mention the numbers for this device, but I would have to guess a few seconds otherwise it could get false readings from drums or the like.

In general, the biggest limitation on just about all AGC algorithms I've worked with is that they choke whenever the input signal goes to zero. They normally work by using a feedback control system where average power is measured over a period of time and making an adjustment to the gain level based on how the average power compares to the target power level. If there's a gap in between songs coming out of your MP3 player, there's very little power in the signal during that time, and as a result, the amplification level can get turned way up. When the next song starts, it can be very loud and painful on the ears or even damage equipment.
 
 Setting slow attack times or fast decay times can help make it less of a problem and it's unfortunate that the 422 device doesn't have any controls for that. That could be the default setting like Sir HC described so maybe it's not even an issue. There are controls to limit total gain and total output voltage, however, so your other equipment will at least be protected from voltage spikes.

[pip]