Trust but Verify

Posted by Tony Lauck (A) on March 26, 2012 at 08:03:16

In Reply to: RE: How hard should I strive to get maximum signal? posted by tom.dennehy on March 26, 2012 at 04:34:49:

Thanks for the example. This is just one example where audio software may "silently" trash the quality of one's recording. This problem is not unique to Audacity, there were similar problems with earlier versions of Soundforge.

There is no guarantee that any editing feature will not mangle the sound quality. Even more subtle than reducing 24 bits down to 16 are effects like converting to/from 24 bit integer and floating point. Here the conversion from floating point back to integer may add dither noise at an "inaudible" level of -135 dBfs. Unfortunately, under some conditions and on some systems this change of +1 or -1 in individual 24 bit samples may result in an audible difference. One has to trust one's tools to be an artisan, but the rule should be "trust but verify". Verification includes technical measurements (e.g. null tests, spectrum analysis, etc.) and careful listening tests, not casual 30 second A - B comparisons.

Other fun exercises one can play is to use the editing features to deliberately trash a recording in a subtle way and see how much trashing it takes before you hear it. Such things include failure to add dither, moderate amounts of clipping, suboptimal filtering for sample rate conversions, etc.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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Follow Ups Full Thread

Topic - How hard should I strive to get maximum signal? - Phil_in_CA 18:24:04 03/24/12 (21)

Look for the Max Signal Level Prior to Digitizing.................... - Todd Krieger 22:31:40 03/24/12 (1)

RE: Look for the Max Signal Level Prior to Digitizing.................... - Phil_in_CA 09:42:50 03/25/12 (0)

don't record hot in digital - Joe Murphy Jr 21:07:33 03/24/12 (9)

That's what I've heard and read, but ... - Dave Pogue 09:10:51 03/26/12 (5)

RE: That's what I've heard and read, but ... - Tony Lauck 10:52:45 03/26/12 (0)

two possibilities - Joe Murphy Jr 09:47:42 03/26/12 (3)

Thanks, just dragged out the owner's manual. - Dave Pogue 11:21:25 03/26/12 (2)

RE: Thanks, just dragged out the owner's manual. - Tony Lauck 13:05:36 03/26/12 (1)

Thanks again, but ... - Dave Pogue 14:23:52 03/26/12 (0)

RE: don't record hot in digital - Tony Lauck 10:04:35 03/25/12 (2)

RE: don't record hot in digital - tom.dennehy 22:10:39 03/25/12 (1)

RE: don't record hot in digital - Tony Lauck 07:46:43 03/26/12 (0)

Thanks! - Phil_in_CA 19:43:22 03/24/12 (4)

RE: Thanks! - Iron Knee 22:50:27 03/24/12 (3)

RE: Thanks! - Tony Lauck 08:08:28 03/25/12 (2)

RE: Thanks! - Iron Knee 10:21:20 03/25/12 (1)

RE: Thanks! - Tony Lauck 11:01:06 03/25/12 (0)

RE: How hard should I strive to get maximum signal? - Tony Lauck 19:36:23 03/24/12 (2)

RE: How hard should I strive to get maximum signal? - tom.dennehy 04:34:49 03/26/12 (1)

Trust but Verify - Tony Lauck 08:03:16 03/26/12 (0)

Any level above -6 dB uses all the bits ... nt - slider 18:43:08 03/24/12 (0)

Follow Ups

Trust but Verify - Tony Lauck 08:03:16 03/26/12 (0)

Trust but Verify

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