Can somebody please tell me how to create an .ac3 mixdown from a surround mix? I have done it before but not for a while and frankly cannot remember what i did last time? About three years ago! 
You need an ac3 encoder.
Thank you for your reply. Mmm. I have done this before. Must be having a senior moment. I cannot believe that I am the only Cubase user in the world doing 5.1 mixes! Help me out here!
âFrom Hollywood blockbusters to popular TV series â Cubase is the go-to DAW for some of todayâs most successful media composers.â Only thing is it doesnât render audio?
Ok. So what encoder does one use? What do todayâs most successful media composers do? 
But definitely not with Cubase. There was a (separate) dolby digital encoder available for Nuendo some time ago though.
Exporting a 5.1 mix does not mean exporting an ac3 stream. You can of course export a discrete 6 channel file with Cubase
see above
Thank you for your reply.
Yes. After thinking about it further I used a video production program called âVegasâ Platinum. You export six separate files, then render down to .ac3. All a bit fiddly really although it works nicely once you get used to it.
I really get the impression software manufacturers do not want people to use 5.1! They seem to hide it away like it is some sort of esoteric cabal! 
It seems such an obvious feature it surprises me that it not there!
Although the manual for Cubase mentions it, the .wmv export function does not work.
So what do people use? All those successful media composers? 
Nuendo?
So Nuendo does it?
That is a complete program, a lot of dollars for such a simple feature. You mentioned a separate encoder. Is that still available?
If not can anybody recommend an alternative? 
As said, you don´t need ac3 to do 5.1 on DVD. The specs also permit uncompressed PCM up to 7.1
No, not without the additional encoder.
Understood thank you.
So what does Cubase recommend for waht seems to be a very normal and obvious function?
I looked at GitHub - wieslawsoltes/wavtoac3encoder: WAV to AC3 Encoder an audio encoder which generates compressed audio streams based on ATSC A/52 specification which appears to be a download from an unknown source full of buttons and settings with no explanation of what the settings are.
[quote="thinkingcapAs said, you don´t need ac3 to do 5.1 on DVD. The specs also permit uncompressed PCM up to 7.1
quote]
Thank you for your replies.
Thinkingcap makes some kind of point about DVDâs using either PCM audio or .ac3 audio. So what?
So walk me through this. When Steinberg makes Cubase they obviously want people to be able to make DVDs with 5.1 audio. The format has been around for a long time now and many homes and cars use this system. So buy a nice new version of Cubase, cool then when it is time to make a DVD you wander round the internet looking at dodgy third-party geek rooms so you can get the audio on to the DVD? Is this Steinberg or Microsoft?
Is there anybody on this forum who makes DVDâs who can tell me what they normally do?
I will say again though I am surprised that a company that advertises that its products are used by todayâs most successful media composers on Hollywood blockbusters to popular TV series does not seem to have included any [working] functionality to make a DVD. What is going here? Are there copyright or licensing issues or have they just not thought about it?
I think there are licencing issues (Dolby). the link I posted is apparently a popular free utility. If you want better you will have to pay.
First of all: Are you talking about DVD-Audio or DVD-Video? DVD Audio does not allow Dolby digital at all anywayâŚ
For DVD-Video, you can use whatever is suitable for your need. It´s not like Red book audio CD, where the files have to be 16 bit / 44,1 kHz. The DVD Video has a max. data rate for both video and audio, you can decide yourself, how you use it - higher audio quality - lower video quality. ac3 is a lossy copmpression codec, PCM is lossless.
No, Steinberg provides the means to create audio that can be used further. Just as you can´t create Audio CD´s you can´t create DVDs (neither video, nor audio) - Wavelab can create Audio CD and -DVD.
As said, you can mix down a discrete 5.1 file, which can be put on a DVD audio or video in uncompressed PCM format without problems.
If you want ac3, then like split says, you pay license fees to Dolby when getting an âofficialâ encoder, which might be one of the reasons, it´s not included in CubaseâŚ
Thank you for your reply! 
Problem solved.
for the benefit of other forum users our initial problem was we did not set the project settings in Architect[DVD software] to 5.1. Sorry about that. Once we fixed that setting we have successfully burnt a DVD using a discrete WAV file and also a WMV file.
We also had the opportunity to compare these files with AC3. AC3 rendered in surround but the audio quality was poor, with each channel heavily compressed and in-yer-face. Quite cool if you like but the results from the WAV and WMA formats are very clean.
Interestingly there seems to be a bug in the WMA export setting.
Set up a surround project
File/Export/Audio Mixdown/File format/Windows Media Audio File then Codec Settings/ General: 44.100 kHz, 16 bit, 5.1 channel, / Encoding Scheme: Constant Bitrate, 440 kbps, 44kHz, 5.1 channel 16bit CBR/OK.
Export : error message: NS_E_AUDIO_NOT_INSTALLED/OK
Dialog box opens: File exists already! /Create Unique Name.
Then everything works!
So it appears the error message: NS_E_AUDIO_NOT_INSTALLED/OK is a false alarm.
You just need to press the export button twice!
Many thanks for your patience thinkingcap and Split.
I saw this error message discussed in another post so I will ask them to try this fix.
On a Mac, I use Apple Compressor. for AC3 or discreet PCM, 6- channel compression.