5.1 an 7.1 surround playback issues

I have a windows 10 system. I am using VLC media player. I
output hdmi to a denon receiver.
I created a project to use test tones to check my channels. The preference setting for export was set to allow multi channel export. I
have created both wav and ac3 files and neither decodes the center ,subwoofer , and surround channels correctly. All the sound is still sent to the left and right channels. What have I missed?

Audacity playback is currently limited to mixing down tracks to mono or stereo (two channels). See http://manual.audacityteam.org/man/faq_playback.html#multi-channel. You should be able to configure your sound card to duplicate left and right to other channels, such as sending normal stereo bass to the subwoofer.

Do you want to “vote” for multi-channel playback support in Audacity? Voting does not make it happen, but we take votes into account when considering new features.


Sorry, I was a bit vague. I export the audio as 6 channel but when I play the exported .wav or .ac3 file it plays all channels but only thru the left and right speakers. I need to create test tomes and bursts for each speaker (5 and subwoofer). :smiley:

Exactly where are you playing that file? Are you sure that application supports multi-channel playback?

It may be best to test the file in Windows Sound or in the Control Panel of your sound card.


I believe HDMI can only do stereo, or Dolby AC, not multi-channel. So you’d need te re-encode your 6 channel audio to an AC3 stream.

There is a DirectShow AC3 encoder for Windows, but it’s gone in Win 10. Besides, it only encodes stereo, so it’s of no use.

ffmpeg can encode AC3, I think, but I have no clue how or if this is implemented in Audacity. My Audacity grinds to a halt when I open two windows and do this kind of test. And it also seems to add dithering, which can be a pita if you’re doing test signals. Have a look:

On the left is the export, on the right the original test recording.

That does not appear to be correct according to https://en.wikipedia.org/wiki/HDMI#Audio.2Fvideo and other references. It may be true that multi-channel is not a mandatory part of the standard.

On Windows, Audacity with FFmpeg 2.2.2 can export up to six channels of AC3.

Which version of Audacity does that? Is the problem having a lot of tracks?

Not really a surprise, considering you have a 32-bit project, but you can turn off high-quality dither that is used for export in Quality Preferences.


Quote from Wikipedia

For digital audio, if an HDMI device has audio, it is required to implement the baseline format: stereo (uncompressed) PCM. Other formats are optional, with HDMI allowing up to 8 channels of uncompressed audio at sample sizes of 16-bit, 20-bit and 24-bit, with sample rates of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz and 192 kHz.

HDMI can in theory do 8 channels, but some computers don’t have audio on HDMI outputs. No receiver I’ve seen has anything more than stereo and AC3. In fact, the only HDMI device I’ve ever seen that supports multi-channel, was a Black Magic Design HDMI converter that does anything to and from HDMI. It’s a professional converter, worth a 1.000$ and not hampered by copy bit protection.

And I’ve never seen HDMI do 192 kHz with 8 channels. I don’t think it is technically possible, even.

That’s why I believe consumer devices don’t support multi-channel audio.

On OSX too. I use that sometimes.

Audacity 2.1.2 on Mavericks, this time with 2 windows, each 6 channels (the same test file before and after export).

I know Gale. It’s just that, in this case, there’s no dithering needed as there is no sample rate conversion. Some DAW’s seem to be intelligent and avoid needless dithering. And it was just a warning if the OP is making test signals, as it can screw with the outcome.

I’ve never made an AC3 file with Audacity, but I’ve successfully converted 6 mono WAV files to a 5.1 Channel AC3 using [u]wavtoac3encoder[/u].

I’ve also never tried playing the stand-alone AC3 file… It’s always been part of a DVD project.

A small correction: Dithering has nothing to do with “sample rate”.

Dither is used to eliminate quantization noise when converting the “sample format” from a higher bit-resolution to a lower bit-resolution. If the sample format is not changed, or is changed from a lower bit-resolution to a higher bit-resolution, then dither is not required and should not be applied.

Thanks, Gale. Didn’t know that.

I’ve always believed it was needed when doing SRC too. One’s never too old to learn, even at my age :smiley:

FINALLY after much screwing around, I have a solution that might be helpful to others. Here is what worked.

In Control panel → sounds → properties ->advanced, select a default format that is at least 16 bit 96000 HZ (studio quality).

Even though Control Panel ->Properties (button) ->Supported Formats (tab) Encoded formats (list) shows lots of DTS and dolby formats, unless you set this bit rate high enough, Windows in its “glorious” human interface design forces default sound to stereo (without telling you why) if the bit rate is not high enough.

After you set a high enough bit rate a configure button appears on the control panel → sound display letting you select the numbers of speakers and test them. Outputting multi channel sound from Audacity no maps correctly to speakers.

FLAME! With 40+ years writing real time control software and interfaces, I am always amazed at the disorganized and even arcane things Microsoft lets leak thru.

Thanks to all who tried to help.

Many thanks for letting us know what solved it for you.

It’s also possible it is a driver issue rather than a Microsoft issue.

By the way, Hz is sample rate, not bit rate or bit depth.