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5.1 weirdness

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5.1 weirdness

Postby ef37a » Sat Oct 20, 2018 7:34 am

I am playing around with a Panasonic DVD player/amp and it seems to work very well but I have a "spacial anomaly" with sound from computers.

I am listening now to R3 from my TV (or a Freeview recorder) via an optical link. Nice sound and the centre channel* seems well balanced against the two LR speakers, sub is on minimum. However, when I jack in the output of either my laptop or a feed from a desktop PC, from an ESI 1010e card, the centre channel all but disappears and this effect happens with the front 3.5mm jack on the Panasonic or the AUX RCA inputs at the rear. Even a solidly mono announcer is not coming from the centre speaker but leaps behind the telly!

This is not a "phase" problem because of course all the speakers connection are the same for each source and there is no loss of bass, in fact the sound quality is virtually the same (there is several seconds time difference!)

Any ideas?

*The supplied centre speaker was bog awful! I have made a new box with a modest 100mm bass/mid unit and Audax tweeter. I have a fifty quid Scan Speak drive unit coming. Today I hope!

Dave.
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Re: 5.1 weirdness

Postby Kwackman » Sat Oct 20, 2018 8:39 am

I'm not sure if this helps your problem,, but "Blits" tone would confirm your speaker balance.
It's downloadable from a few places, including..

https://www.digitalproductionpartnershi ... _up_tones/

and this explains what it is.
https://ips.org.uk/encyclopedia/blits-b ... -surround/
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Re: 5.1 weirdness

Postby Kwackman » Sat Oct 20, 2018 8:44 am

ef37a wrote:However, when I jack in the output of either my laptop or a feed from a desktop PC, from an ESI 1010e card, the centre channel all but disappears and this effect happens with the front 3.5mm jack on the Panasonic.

Forgive me if I've mis-understood this.
But, if you are using a stereo source (3.5mm jack), the the centre channel SHOULD disappear, along with the rear speakers too?

EDIT, I was going to try to combine both posts into one, but failed!
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Re: 5.1 weirdness

Postby ef37a » Sat Oct 20, 2018 9:01 am

Kwackman wrote:
ef37a wrote:However, when I jack in the output of either my laptop or a feed from a desktop PC, from an ESI 1010e card, the centre channel all but disappears and this effect happens with the front 3.5mm jack on the Panasonic.

Forgive me if I've mis-understood this.
But, if you are using a stereo source (3.5mm jack), the the centre channel SHOULD disappear, along with the rear speakers too?

EDIT, I was going to try to combine both posts into one, but failed!

You are forgiven, hurts my head too! The feed from the TV is stereo. A TV programme or BBC radio. As I expected the centre channel is simply an LR sum and any "stereo" effect comes from the LR speakers and the signal from the latter stops for a central, mono link person's voice (I suppose there is some L&R but way down) . If I play a proper 5.1 source DVD, Jurassic Park I get the full Monty, sub, centre, and L&R (not bothered with rears yet) .

So, all is cool for TV sources and DVD 5.1 but out of a PC the centre channel goes away, sort of "reverse Kareoke"!

Just tried a music CD, Exile on Main Street. As I would expect, Mr Jagger is coming from the centre speaker.

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Re: 5.1 weirdness

Postby Kwackman » Sat Oct 20, 2018 9:08 am

Hmm, for a stereo signal I would expect the centre speaker to be mute. If yours isn't mute, I'm probably wrong, again! My old thinking is that stereo should be LR, not LCR.
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Re: 5.1 weirdness

Postby blinddrew » Sat Oct 20, 2018 9:56 am

I'm many years out of the industry now but stereo always used to be LR, some of the smarter amps would bypass all the surround processing entirely. You used to be able to buy processors that just provided the av in and out and the 3.1 channels to add to your existing stereo amp.
Waffling now, in summary, i wouldn't expect anything from the centre in stereo mode.
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Re: 5.1 weirdness

Postby ef37a » Sat Oct 20, 2018 10:03 am

Kwackman wrote:Hmm, for a stereo signal I would expect the centre speaker to be mute. If yours isn't mute, I'm probably wrong, again! My old thinking is that stereo should be LR, not LCR.

I think you are right K. I have a theory! The optical input from the TV and the CD/DVD source both go through the 5.1 processor and thus L&R are summed for a centre channel. The front and back analogue inputs do not however go to the 5.1 matrix and this do not get summed and routed to centre.

This is a pain and a bother. I bought the system partly BECAUSE I wanted a clear, dialogue source because I am well mutton. I am not too upset, at least TV sound is way better and I get centre sound for that (the speaker I built is a bit too "plummy" for me atmo' but I am hoping the S'Speak will help there plus some fiddling with crossovers. Maybe another tweeter?)

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Re: 5.1 weirdness

Postby Kwackman » Sat Oct 20, 2018 10:21 am

ef37a wrote:The optical input from the TV and the CD/DVD source both go through the 5.1 processor and thus L&R are summed for a centre channel.

This still feels wrong to me.
In my world (other worlds are available and may be more in touch with reality) L & R should only be combined if you want mono, and this mono should never be combined with L + R stereo.
It MAY be combined with an S signal (L - R) to recreate the stereo field.

So, that got me thinking, is there a switch (or in these days more likely to be a setting in a menu somewhere) that enables/disables a "phantom" centre speaker?

I'd a very short relationship with a domestic 5.1 system, and I remember having a switch like this where the centre speaker was muted (along with the rears) for stereo sources.
Anyone mixing in stereo is only going to be using L + R speakers and assuming a phantom centre.
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Re: 5.1 weirdness

Postby Hugh Robjohns » Sat Oct 20, 2018 10:23 am

The problem here appears to be understanding what your 5.1 system is actually doing.

The issue is that you have a 5.1 speaker array (left and right front, centre, left and right back/side, and a subwoofer) on the output side, and an indeterminate number of channels on the input side.

A straight professional 5.1 system expects six discrete input channels, and routes them directly to their respective outputs. In many cases there may be a integrated bass management system, too, to strip off the low end from the five main channels and combine that content with the LFE (low frequency effects) signal before feeding the mix to the subwoofer. (This is called 'bass management')

Domestically, 5.1 source material might come from a DVD or bluray player, or from an HDTV channel, most usually in the form of a Dolby Digital formatted signal, often carried over a TosLink or coax S/PDIF connection.

However, many consumer 5.1 boxes have some sort of auto-detect system to decide what the source format is and allocate its source channels to the output speakers 'appropriately',

That might mean sending a stereo source just to the left-right from speakers, in the traditional way... Or it might involve synthesising a pseudo centre channel either from a simple stereo sum, or by using a Trifield algorithm, etc. or it might involve generating fake centre and rear channel information using a Dolby Pro.Logic, DTS Neo, or Hafler-style matrix... or even just smother everything in artificial reverb in an effort to simulate some kind of 'jazz club' effect!

You'll need to read the 5.1 processor's manual and configure the unit appropriately to find the best solution for you... But I don't hold out too much hope of getting clean dialogue from the centre speaker and underlying music from the left-right channels from broadcast stereo sources.

Using Dolby's PLII decoder might make a reasonable stab at it, but there will be artefacts when it gets tripped up... which it will!

...and then there are the 5.1 processor's internal routing arrangements that may well bypass the 5.1 digital decoding system for some 'direct' analogue inputs. Again, you'll need to RTFM.

H
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Re: 5.1 weirdness

Postby ef37a » Sat Oct 20, 2018 11:28 am

Oh! The F M has been well R'ed I can assure you Hugh!

Yes, I am sure you are right, the 5.1 system simply does not produce a centre channel for a basic analogue stereo input. Clearly optical digital "tells" it to do so even when the source is basic stereo. Nuisance.

I suppose the S/PDIF out of the ESI will work as I want? I shall try that next but then I shall have the problem of source selection. There is only one optical input. I dare say somebody makes an optical switch? I dare say they are pricey as well!

The unit is a Panasonic SA-HT855 and I paid peanuts for it from a charity shop so I am actually quite pleased with the performance I do get, vast improvement on telly sound!

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Re: 5.1 weirdness

Postby Hugh Robjohns » Sat Oct 20, 2018 1:20 pm

ef37a wrote:...the 5.1 system simply does not produce a centre channel for a basic analogue stereo input.

There may well be a way of making it process a two-channel signal into a 5.1 formatted output, because a lot of legacy media will have Dolby Stereo tracks (LtRt) which need to be decoded with a Dobly Pro.Logic decoder to regains the matrix-encoded LCRS surround sound track. And those legacy machines (VHS cassettes etc) will generally only provide an analogue stereo output...

A quick look at the manual suggests that pressing the DPII button should do what you want with stereo input sources.

H
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Re: 5.1 weirdness

Postby ef37a » Sat Oct 20, 2018 6:28 pm

Hugh Robjohns wrote:
ef37a wrote:...the 5.1 system simply does not produce a centre channel for a basic analogue stereo input.

There may well be a way of making it process a two-channel signal into a 5.1 formatted output, because a lot of legacy media will have Dolby Stereo tracks (LtRt) which need to be decoded with a Dobly Pro.Logic decoder to regains the matrix-encoded LCRS surround sound track. And those legacy machines (VHS cassettes etc) will generally only provide an analogue stereo output...

A quick look at the manual suggests that pressing the DPII button should do what you want with stereo input sources.

H

Nope, that button just throws "ERROR" on the display. Ho-hum, I have nice TV sound now so I can live with the loss.
Thank for all your inputs.

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Re: 5.1 weirdness

Postby ef37a » Tue Oct 30, 2018 12:13 pm

Update and one solution.

I connected the laptop to the JVC smart tv via HDMI. Now the optical signal from the TV is encoded such that I get a centre channel and sub.

Initially the HDMI connection only gave me picture, no sound but a Google search came with a procedure, ran it. Glorious sound!

I wanted the HDMI link for another purpose to do with guitar amps and shall post a link to that later.

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