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5.1和立体声的下混是如何工作的？

5.1下混设置：
这些选项应用于监听，同时也作为元数据写入了.atmos文件并应用于编码Dolby Digital Plus JOC。
这些选项可以分别为监听/元数据和Re-render进行独立设置。Trims的数值应用于5.1下混。

Standard 标准（Lo/Ro）- 默认值
先渲染成7.1，再通过系数下混为5.1
Ls = 0dB x Lss + 0dB x Lrs
Rs = 0dB x Rss + 0dB x Rrs

Dolby Pro Logic IIx
先渲染成7.1，再通过系数下混为5.1
Ls = Lss + ( -1.2dB x Lrs ) + ( -6.2dB x Rrs )
Rs = Rss + ( -6.2dB x Lrs ) + ( -1.2dB x Rrs )

Direct render with room balance
使用Room Balance（房间平衡）直接渲染 （在v3.5版本以前Room Balance称为Warp）
使用不通过下混7.1的方式将杜比全景声内容直接渲染成5.1，这需要使用新的杜比渲染算法，它可以有效减少Object在房间前后运动到一半时，由于幻象声源造成的梳状滤波效应。 Room Balance表示的是声音在房间中部到后部之间运动时渲染器的处理方式，他确保声音位于中部到后部时，在各个环绕扬声器都表现为恒定的值，除非进入房间前部，否则不会产生任何幻象声源。

Direct render 直接渲染
用渲染器中的渲染引擎直接将全景声内容渲染成5.1，用环绕扬声器和前置扬声器形成的幻象声源在中央听音位置精确地重建声场。

除了直接渲染，所有的立体声下混选项均是先从全景声渲染的7.1下混一个5.1，然后用和2.0消费产品一样的方式从5.1下混到2.0。上面所选的5.1下混选项会影响随后的5.1到2.0下混。

Lo/Ro - 默认值 ：通过以下系数将5.1下混成立体声

Lo = L + (–3 dB × C) + (–3 dB × Ls)
Ro = R + (–3 dB × C) + (–3 dB × Rs)

Lt/Rt (Pro Logic II): 通过以下系数将5.1下混成立体声
Lt = L + (–3 dB × C) – (–1.2 dB × Ls) – (–6.2 dB × Rs)
Rt = R + (–3 dB × C) + (–6.2 dB × Ls) + (–1.2 dB × Rs)

Lt/Rt (Pro Logic II) w/Phase 90: 通过以下系数将5.1下混成立体声
Lt = L + (–3 dB × C) – (–1.2 dB × Ls) – (–6.2 dB × Rs)
Rt = R + (–3 dB × C) + (–6.2 dB × Ls) + (–1.2 dB × Rs)

在使用Ls/Rs进行下混之前应用90度的相位偏移，可以减少信号抵消，提升声像定位，启用正确的矩阵解码。我们强烈建议您在任何LtRt下混中使用90度相位偏移

How do the 5.1 and Stereo downmix settings work?

2021-1-4
5.1 downmix settings:
This selection is used for monitoring and also written to the .atmos file set as metadata and applied during encoding to Dolby Digital Plus JOC.
This selection can be independently set for monitoring/metadata and re-renders. Trims values are applied to the 5.1 downmixes.

Standard (Lo/Ro) - default: renders to 7.1 and then downmixes to 5.1 using the coefficients:
Ls = 0 dB × Lss + 0 dB × Lrs
Rs = 0 dB × Rss + 0 dB × Rrs

Dolby Pro Logic IIx: renders to 7.1 and then downmixes to 5.1 using the coefficients:
Ls = Lss + (–1.2 dB × Lrs) + (–6.2 dB × Rrs)
Rs = Rss + (–6.2 dB × Lrs) + (–1.2 dB × Rrs)

Direct render with room balance: renders from Dolby Atmos to 5.1 (without downmixing via 7.1) by
applying an updated Dolby rendering algorithm that reduces the comb filter effects associated with
phantom imaging of objects positioned halfway between the front and rear of the room. Warp refers
to how the Renderer deals with content that is panned between the midpoint and rear of the room.
With warp, the content is presented at a constant level in the surround speakers between the rear
and midpoint of the room, avoiding any need for phantom imaging until it is in the front half of the
room.

Direct render: renders from Dolby Atmos to 5.1 (without downmixing via 7.1) by using the
rendering engine in the Dolby Atmos Renderer to accurately recreate the sound field at the central
listening position using phantom imaging between the surround speakers and front speakers.

Stereo downmix settings:

All the stereo downmix options except Direct Render are created by first creating a 5.1 downmix
from the 7.1 render of .atmos content, and then downmixing from 5.1 to 2.0 in the same manner as 2.0
consumer products. The choice of the 5.1 downmix method above affects the subsequent 5.1 to 2.0 downmix.

Lo/Ro - default: Downmixes from 5.1 to Stereo using the coefficients:
Lo = L + (–3 dB × C) + (–3 dB × Ls)
Ro = R + (–3 dB × C) + (–3 dB × Rs)

Lt/Rt (Pro Logic II): Downmixes from 5.1 to Stereo using the coefficients:
Lt = L + (–3 dB × C) – (–1.2 dB × Ls) – (–6.2 dB × Rs)
Rt = R + (–3 dB × C) + (–6.2 dB × Ls) + (–1.2 dB × Rs)

Lt/Rt (Pro Logic II) w/Phase 90: Downmixes from 5.1 to Stereo using the coefficients:
Lt = L + (–3 dB × C) – (–1.2 dB × Ls) – (–6.2 dB × Rs)
Rt = R + (–3 dB × C) + (–6.2 dB × Ls) + (–1.2 dB × Rs)
Applies a 90 degree phase shift to Ls/Rs prior to feeding the downmix which reduces undesirable signal cancellation,
improves imaging, and enables proper matrix decoding. It is strongly recommended to use the 90-degree phase shift for
any Lt/Rt downmixes.