Focusing on the title and steps to reproduce, I contend that this is correct behaviour.
1. If rectangular dither is used on silence, 0.99 bits of noise are added, and quantization entirely eliminates the dither noise, so the silent audio is exported perfectly. 2. Whilst open, the '16bit' track is held as float values and operated on as float values. There may be an envelope, panning and gain applied, which take the intermediate data outside the values 16 bit can represent. Just as Audacity cannot operate on Mp3 audio without round-trip losses, so too, with its current architecture, Audacity cannot operate on 16 bit without using float as an intermediate. That's an architectural choice, and a good one. Our 16 bit format is held as float whilst in RAM. That is good design. We only pay a 'dither' tax for the extra precision on export or save. An actual 16 bit internal format would be worse, as we would instead pay a 'quantization tax' on every operation on the audio. Since an envelope or gain change IS an operation on the audio as far as the export stage is concerned, we would almost always pay the 'quantization tax' on export rather than as now the (lesser) dither tax. Of course, just as Audacity could have been designed to allow cut and paste and stepped amplification of Mp3 audio without round trip losses, so too Audacity could have been designed to allow cut and paste of 16 bit format without round trip losses. With it's current architecture it comes very close indeed. I'd recommend that when working in 16 bit format users select rectangular dither. That way cut and paste of 16 bit sources including pure silence are unaffected, and at the same time quantization noise on processed or generated audio is handled really well. The shaped dithers may handle the quantization noise very slightly better, but at the cost of disrupting silence. A possible enhancement request is to recommend rectangular dither when 16 bit format is selected as the default in prefs. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/608964 Title: Select-all + Export Selected produces different .wav file To manage notifications about this bug go to: https://bugs.launchpad.net/audacity/+bug/608964/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
