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Why are cinema surround speakers set to -3Db? |
Posted by: Turisu - 2021-10-03, 11:54 AM - Forum: General technical discussions
- Replies (6)
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Is it to compensate for the fact that the front 3 speakers are behind the screen? And if so, is the intention that the audience perceives the levels as the same?
If this is true then the accepted wisdom that cinema DTS rips need to have their surround channels attenuated by -3Db for home viewing would be wrong.
It's interesting when looking at home mixes that are close to their theatrical counterparts as some apply the attenuation and some don't.
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Hello! |
Posted by: Zerimar - 2021-10-03, 05:12 AM - Forum: Presentation
- Replies (1)
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I’m new! I’ve always been fascinated with film restoration ever since seeing mini features on how the original Star Wars film trilogy was restored back in the early 90s ?
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Setting the standards: audio capture, release, comparison |
Posted by: spoRv - 2021-10-01, 06:32 PM - Forum: Restoration guides
- Replies (3)
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I guess we need to set some standards here, about audio capture, release, comparison.
There are my guidelines - please let me know if you agree or if not, state reason and alternative.
AUDIO CAPTURE
PCM tracks:
- if a bit-perfect capture card is available, capture it at 44.1kHz/16bit
- if a bit-perfect capture card or digital input is not available, capture it at 48kHz/24bit from analog outputs to avoid second conversion
Analog tracks: capture at 48kHz/24bit
AC-3 tracks: bit-perfect capture card with digital input and AC-3 demodulator are needed; capture at 48kHz
DTS tracks: bit-perfect capture card with digital input; capture at 44.1kHz/16bit
AUDIO RELEASE (captured tracks)
PCM tracks:
- if captured with a bit-perfect capture card, release as 44.1kHz/16bit is mandatory; a 48kHz/16bit conversion is allowed
- if captured through analog outputs, release as 48kHz/16bit
Analog tracks: release as 48kHz/16bit
AC-3 tracks: release as 48kHz/XXbit - where XX is the number of bit of the AC-3 track when de-encapsulated
DTS tracks: release as 44.1kHz/16bit is mandatory; a 48kHz/16bit conversion is allowed
Release formats: WAV, FLAC; DD ONLY for untouched AC-3 captures; DTS ONLY for untouched DTS capture
Note: releasing captures at more than 16bit is useless, while capturing at 96kHz is not only useless, but can also be harmful, introducing unwanted high frequencies and forcing the capture card to use slightly less dynamic range than 48kHz.
AUDIO CONVERSION
Question: what about captured track levels? Set the maximum at 0dB? Set the maximum according to other tracks if in sync?
AUDIO RELEASE (other tracks)
The following guidelines could be applied only if the audio is edited; if the track is untouched, release it "as is".
Dolby Digital: while professional encoders have good quality, the free ones are noticeable less refined; hence if you decide to release tracks in Dolby Digital using a free encoder, use a higher bitrate than the source
Examples:
DD source → DD release (minimum bitrate):
- 192kbps → 256kbps
- 256kbps → 384kbps
- 384kbps → 448kbps
- 448kbps → 640kbps
- 640kbps → release as DTS or lossless
- DD EX → release as DTS-ES or lossless
DD+ source → DD release (minimum bitrate):
- 192kbps → 384kbps
- 384kbps → 640kbps
- 448kbps or higher → release as DTS or lossless
- 6.1ch or more → release as DTS-ES or lossless
DTS: avoid to use half rate, as it has a rolloff at high frequencies; if you need to have small size track, use DD 640kbps instead.
Examples:
source → DD release (minimum bitrate):
- DD/DD+ 448kbps or higher → DTS 1536kbps
- DTS 1536kbps → release lossless
Lossless: PCM, Dolby TrueHD and DTS-HD MA sources should be released as well as lossless; anyone of the three main format could be used - PCM, TrueHD, DTS-HD MA - even if different from the source; FLAC is accepted as added option, or only when an audio-only track is released
Bit depth and frequency: I continue to think that releasing track at more than 16bit is useless and more than 96kHz could be harmful; even if someone could theoretically manage to hear the dynamic difference of 98dB that 16bit allowed - maybe using great headphones and risking deafness - I bet it is not possible, using any speaker system, listening to a movie audio track.
AUDIO COMPARISONS
To show audio tracks features graphically, it's possible to post waveforms and spectrums; we have only to find a standard way to do it.
As not everyone could have access to paid tools, I guess we should stick to free software; I'd go with Audacity for waveforms and Spek for spectrums; so we have comparable screenshots.
Set Audacity fullscreen, tracks as wide and high as window, waveforms in dB, meter dB range at (I guess 60dB is the minimum; 96dB is already too much, while 36dB is not enough; sadly someone is posting screenshots from other software with range set at only 24dB; in that way, most of the track seems completely silent!!!); set Spek fullscreen too; release image at 1920px width (scale it if your resolution is bigger or smaller); height is dependant from the number or tracks - for example if you want to show more details in an 8-channel track, you could take two (or more) screenshot and glue them together as a single one.
Note: is there any Nyquist programmer? Would be nice to modify a plugin to get stats similar to professional softwares - nothing fancy, only highest and lowest peaks, noise floor, track length etc.
EDIT: written an article about waveform comparisons - contains different dynamic range from 18dB to 24bit full scale 145dB:
http://blog.sporv.com/comparing-tracks-waveforms/
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Hello |
Posted by: kli4554ilk - 2021-10-01, 07:42 AM - Forum: Presentation
- Replies (1)
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Hello!
New here but always loved fan restorations. I've lurked here for a little and decided to finally join. I also followed the 4k77/4k83 and am of course waiting on 4k80. Amazing work people are doing!
Hopefully in time I can contribute as well
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