LtRt / Lt-Rt / Left total Right total / Dolby Stereo / Pro Logic Compatible

stereo mix loro dolby pro logic dolby surround prologic lcrs left center right surround

Left total/Right total – a two-channel audio format that contains matrix-encoded surround sound information, allowing compatible decoders (Dolby Pro Logic) to extract center and surround channels from the stereo signal while remaining compatible with standard stereo playback.

What is LtRt?

LtRt (Left total/Right total) is a matrix-encoded two-channel format that contains surround information. Compatible decoders like Dolby Pro Logic can extract center and surround channels from the stereo signal.

Basic Principle

Aspect	Description
Meaning	Left total/Right total
Channels	2 (with encoded data)
Surround Info	Matrix-encoded
Decoding	Pro Logic compatible

LtRt vs. LoRo

Aspect	LtRt	LoRo
Surround Info	Yes (encoded)	No
Decoding	Possible	Not necessary
Complexity	Higher	Simple
Phase Relationship	Critical	Less critical

Matrix Encoding Principle

Channel	Encoding
Center	L = R (in phase)
Surround	L = -R (out of phase)
Left	L only
Right	R only

Encoding Formula

Source	Lt	Rt
L	1.0	0
R	0	1.0
C	0.707	0.707
S (Mono)	0.707	-0.707

Decoding (Pro Logic)

Step	Description
Sum	Lt + Rt = Center
Difference	Lt - Rt = Surround
Steering	Directional recognition
Output	L, C, R, S

Pro Logic Versions

Version	Description
Pro Logic	Original, mono surround
Pro Logic II	Stereo surround
Pro Logic IIx	6.1/7.1 expansion
Pro Logic IIz	Height channels

Application Areas

Area	Usage
TV Broadcast	Standard delivery
DVD	Stereo track
Streaming	Surround compatible
Archiving	Compact format

Advantages

Advantage	Description
Backward Compatible	Works as stereo
Surround Potential	With decoder
Compact	Only 2 channels
Established	Proven technology

Disadvantages

Disadvantage	Description
Channel Separation	Limited (~30dB)
Phase-Critical	Can create artifacts
Mono Surround	In basic Pro Logic
Compromise	Not like discrete 5.1

Creation

Method	Description
DAW Encoder	Plugin
Hardware	Dolby encoder
Console	Downmix matrix
Software	Dedicated tools

Software Tools

Tool	Function
Dolby Encoding	Professional
Pro Tools	Downmix options
Nuendo	Encoder integrated
Plugin Solutions	Various

Quality Control

Check	Method
Decode Test	Check Pro Logic
Phase Check	Correlation meter
Mono Test	Cancellations?
Dialogue	Center extraction

Phase Problems

Problem	Cause
Dialogue disappears	Phase error
Surround bleeding	Incorrect matrix
Mono collapse	Out-of-phase material
Pumping	Steering artifacts

Delivery Requirements

Platform	Specification
Netflix	LtRt required
Broadcast	Standard
Streaming	Often needed
Home Video	As an option

Technical Specifications

Parameter	Typical Value
Sample Rate	48kHz
Bit Depth	24-bit
Loudness	-24 LKFS
True Peak	-2 dBTP

Cinema History

Year	Development
1976	Dolby Stereo introduced
1987	Pro Logic
2000	Pro Logic II
Today	Still relevant

Workflow in Post

Phase	Activity
5.1 Mix	Surround version
LtRt Encode	Matrix downmix
QC	Decode verification
Delivery	Along with LoRo

Comparison to Discrete 5.1

Aspect	LtRt	Discrete 5.1
Channels	2	6
Separation	~30dB	Complete
File Size	Small	Large
Quality	Good	Best

Best Practices

Practice	Reason
Check decode	QC essential
Observe phase	Avoid artifacts
Compare with LoRo	Consistency
Documentation	For acceptance

Today

LtRt remains an important component of professional audio deliveries, even though discrete surround formats dominate. The ability to transport surround information in a 2-channel format makes it valuable for backward-compatible playback. The correct creation and quality control of LtRt are part of the standard repertoire of any audio post-production.

From the crafts

Perspectives

Cinematographer

LtRt ist die clevere Surround-Stereo-Version. Beim Abspielen über Pro Logic kommt wieder Surround raus – wichtig für kompatible Deliveries.

Director

LtRt gibt meinem Film Surround-Potenzial auch in Stereo. Ein guter Decoder bringt die räumliche Dimension zurück – das ist der Kompromiss für 2-Kanal-Systeme.