5.1 Audio files

[blueznl]

Ages ago I fooled around with VCD's and visited this forum, and I've returned as I'm struggling with creation of proper 5.1 audio files for test purposes. I've been able to put some 5.1 wav / ac3 files to regular CD, and some of them would play, but not always as I expected. Here's what I managed thus far:

Problem 1 - 5.1 mix in Adacity - solved, it works, I can export 5.1 AC3 files
Problem 2 - 5.1 over SPDIF from my laptop to my amp - can't get it to work, dunno why
Problem 3 - Nero AC3 plugin - solved, I can burn AC3's to audio CD's
Problem 4 - I don't understand how audio files are recognized
Problem 5 - well, more of a question - what does the surround led on my amp make light up?
Problem 6 - BeSweet - solved, managed to create some files using BeSweet + BeSure

Here's the thing: you can find some files on the internet in .WAV format, containing DD or DTS information. Try, for example, the sample files on Kelly Industries, or those on masterpinguin.de

Now it gets interesting: currently nothing played on my laptop over SPDIF is recognized by my amp as surround, this may be caused by the laptop though... But... there is some inconsistent behaviour when playing back files from a CD. Here's what happens when I burn the downloaded .WAV or created .AC3 files on CD and play it back on my kit:

kelly industries wav file (DD) -> audio track on CD -> digitaal to amp -> works and is recognized
kelly industries wav file (DD) -> audio track on CD -> analoog to amp -> doesn't work
own creation ac3 file (5.1) -> audio track on CD -> digitaal to amp -> works but isn't automatically recognized
own creation ac3 file (5.1) -> audio track on CD -> analoog to amp -> works but isn't automatically recognized

To play back my own AC3 in surround mode I have to change the setting of my amp to 'ProLogic', 'II', 'Neo', 'Multi' or whatever, but it won't recognize my own tracks in 'AFD Auto' mode. Appearently there is a difference

Where to go next? Convert to a different bitrate and try to burn them as a DVD? I'm getting just a tiny little bit lost...

[El Heggunte]

Hi there.

First of all, you should NOT be using Nero.
This is what I would do, if I were you:

1) create proper AC3 files with Aften
(probably Audacity is fine too, but I've never liked this latter)

2) use spdifer.exe (available @ the AC3Filter web site) for
generating proper .WAV files

3) create a regular Audio-CD with these .WAVs

[COMMAND-LINE]
Spdifer
=======
This utility encapsulates AC3/DTS/MPEG Audio stream into SPDIF stream
according to IEC 61937

This utility is a part of AC3Filter project (http://ac3filter.net)
Copyright (c) 2007-2009 by Alexander Vigovsky

Usage:
  spdifer input_file output_file [-raw | -wav]

Options:
  input_file  - file to convert
  output_file - file to write result to
  -raw - make raw SPDIF stream output (default)
  -wav - make PCM WAV file with SPDIF data (for writing to CD Audio)
[/COMMAND-LINE]

[Nelson37]

Anything played over two-channel analog connections will lose the full 5.1 channels, any "surround" will be simulated.

Downmix to 2-channel stereo PCM is often the default on SPDIF connection.

A "DD-Wav" file is a Digital file, meant for SPDIF output. DD-Wav technically is a 2-channel PCM file, but it contains the data for full 5.1. Be very careful trying to output a DD-Wav thru an analog connection, you should get rapidly pulsing static that is Very Loud. Speaker-damaging loud, DO NOT USE HEADPHONES.

There needs to be a setting on soundcard or playback software for Raw SPDIF output, or Output as AC-3, or something similar. AC3Filter can do this for you.

Note the two options for output on the software above. The first, I think, is DD-Wav output. I have no idea what exactly the second one is. "PCM WAV file with SPDIF data".

[El Heggunte]

Note the two options for output on the software above. The first, I think, is DD-Wav output.

I have no idea what exactly the second one is. "PCM WAV file with SPDIF data".

It's the same as the first one, plus an adequate .WAV header
(channels = 2, sampling frequency = 32 / 44.1 / 48 kHz).

P.S.: It seems the newest version(s) of AC3Filter

cannot decode SPDIFed MP2 / MP3 anymore

[blueznl]

Nelson, I understand the downmix to two channels is loosing full 5.1 support, I was just wondering if the Dolby encoding mechanisms, once applied to a 2 channel soundstream, would be recognized by the amplifier.

You see, if I enforce the amplifier to support Dolby Surround or something similar, it processes the audio stream, but I was wondering if there was something inside the audio stream that would trigger the amp to automatically detect it's a stream containing surround information, such as a pilot tone or something similar...

[Cornucopia]

kelly industries wav file (DD) -> audio track on CD -> digitaal to amp -> works and is recognized
kelly industries wav file (DD) -> audio track on CD -> analoog to amp -> doesn't work
own creation ac3 file (5.1) -> audio track on CD -> digitaal to amp -> works but isn't automatically recognized
own creation ac3 file (5.1) -> audio track on CD -> analoog to amp -> works but isn't automatically recognized

To play back my own AC3 in surround mode I have to change the setting of my amp to 'ProLogic', 'II', 'Neo', 'Multi' or whatever, but it won't recognize my own tracks in 'AFD Auto' mode. Appearently there is a difference

Where to go next? Convert to a different bitrate and try to burn them as a DVD? I'm getting just a tiny little bit lost...

This tells me that what you're creating on the AudioCD is a 2-channel WAV that is a ProLogic Downmixed vesion of your AC3. Those 4 "responses" are exactly like what would happen with comparing AC3-spdiffed into-WAV vs. AC3-downmixed+converted-"stereo/DS" WAV.

Follow El Heggunte's advice.

Scott

...or read on of my past posts on this very subject...

[Nelson37]

Could you expand a bit on where this conversion takes place? Is the Prologic downmix a default behavior at any point in the chain?

This is the first mention I have seen about output thru SPDIF needing any special header preparation. I thought that if you have a 5.1 file and just set output to SPDIF, it recognized and played as such, if all the playback software supported it.

I thought his 5.1 AC-3 on CD thru SPDIF should have worked. Wait, I read your response again, you're saying the file as written is already downmixed?

Why how who where WTF please tell me more.

[Cornucopia]

It comes down to the mixing engine & the SPDIF driver.

If the driver supports DIRECT AC3 or DTS (or other?) compressed files, your job is easy. However, all older model ports wouldn't do this. Even now, it's not often that it directly supports them.

Why?
Because SPDIF was conceived way back when Digital Audio was just getting started, and in its original incarnation, only considered uncompressed LPCM streams (2). A few of the packet header flags have been subsequently changed to include a "compressed data" stream designation, among other things. So now it's possible.

Without direct support, you have to give the SPDIF port a signal that, while it isn't truly an LPCM WAV file/stream, is "dressed up" to look like one.

So then, either the mixing engine (or a plugin) will process the AC3/DTS stream and packetize it with enough filler to match the standard LPCM bitrate, and do it live,
OR
A program, plugin, transform will act on an AC3/DTS file and create a AC3-WAV/DTS-WAV file that can be played/streamed/ported through the SPDIF just like any other "2 ch WAV" file.

I'm pretty sure that in the OP's narrative, Audacity created a 5.1 AC3, but the NeroAC3 plugin mentioned is usually used to DECODE AC3 in EAC3to. Also, it is supposed to not support 5.1 unless one also includes the Hacked WAV plugin as well. So, without this, my guess is that this is where the downmix occured.

I honestly don't know why the OP followed these steps, since the Kelly's site explains how to create such files. Of course, they don't specify WHICH tools. Minnetonka's Surcode, SonicFoundry's DD SoftEncode, DTS2WAV, AC32WAV, headac3e, and others have been known to work.
But it's probably easier to use that SPDIFER app, since you can leave the usual compression to the regular plugins, and then just apply the WAV padding with that app. Unfortunately, it's probably a one-way process. Don't think it can REMOVE that padding, so always save a clean copy 1st.

...In addition to the Kelly industries site, check out Swedish Radio's Sr 5.1 Multikanal site and HydrogenAudio's site & forums...

blueznl,
A Dolby Surround/ProLogic/PLII file/stream is to all onlookers, a "stereo" file/stream. I doesn't have a "flag" or any other metadata with which to get the Decoder to recognize that it's Dolby encoded. It just has to be switched on manually.

Scott

[El Heggunte]

Unfortunately, it's probably a one-way process. Don't think it can REMOVE that padding, so always save a clean copy 1st.

spdifer.exe doesn't overwrite the input file(s).

As for removing the SPDIF-padding, bsconvert.exe is the way to go.

eac3to works with DTS-WAVs, but does not work with AC3-WAVs.