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Auto limiting in Audacity?, Shouldn't the levels be all over the place?
w1L50n23
post Oct 9 2013, 12:13
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I have done about 20 albums so far and on each (all different genres), the level never has to be adjusted since the first time. Max level is always showing at about -5db. I find it hard to believe that the vinyl levels are matched. I did not set any hard limiters in Audacity, as a matter of fact, I unchecked all effects in preferences so there would be nothing but raw audio. Is there something enabled by default I missed? I would have expected to play each album twice...once to set levels and then to record. I guess the B-part of this question is: maybe this is a good thing?? But I would still like to understand.
Perhaps I have set something in the EMU 1820 Patchmix software...but again I kept it simple and didn't see anything about limiters when I configured.
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AndyH-ha
post Oct 9 2013, 19:41
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Since I don't use Audacity I can't say anything for certain but there certainly should not be any default that modifies the input. Any and every recording application should produce exactly the same result.

The input level is quite variable from one hardware setup to another. Cartridges have significantly different outputs from any given LP. There are differences of at least several dB output from different phono preamps for the same signal level input. Different soundcards will record at different levels for a given input level. However, all of the above should be consistent each time they are used, with the LP being the only variable.

My setup has no variables in the input chain; I cannot adjust input signal level. This has never been a problem so far, for around 750 albums. Recorded maximum peaks for an album mostly fall within about a 6dB range (just a guestimate based on casual observation). I only pay attention to the more extreme cases. The maximum peak has reached about -0.2dBfs two or three times. It has been down around -20dBfs a somewhat larger number of times.
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DVDdoug
post Oct 28 2013, 19:10
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There's no automatic limiting or automatic volume adjustment in Audacity.

I'm a little surprised, but there are physical limitations to how much "wiggle" you can put into a record groove. (To some extent, it depends on playing-time). So, there is some consistency between records and Andy's 6dB range (+/- 3dB) seems about right to me.

I would have expected at least a 3dB difference between your "loudest" & "quietest" record.

You'd might see (measure) more difference if you actually analyze the data to find the actual peak. With Audacity, you can choose the Amplify effect, and it will scan the file and then set the default amplification to whatever gain is needed to bring the peaks up to 0dB. For example, if the peak is -5dB, the default amplification will be +5dB.

Of course a loud "click" can produce a peak that throws-off your "statistics", and maybe clip your preamp. Or if you are already clipping, a loud click can't go any higher.

There could be something clipping in your analog hardware, or you could be clipping your ADC and then reducing the peak/clipping level with record-volume setting after the waveform is clipped.. You can zoom-in to look at the peaks to see if you are getting clipping, or if most of your peaks match within 1dB or less, I'd also be suspicious of clipping.
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