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Digital Stereo to 5.1 convertor needed - any recommendations?


Active Member
I recently purchased the Logitech z906 surround sound system, and while I am very happy with the playback of Dolby Digital and DTS 5.1 tracks, Logitech's own 5.1 upconversion of stereo sources is very poor compared to Dolby Pro Logic encoding.

I'm basically looking for a box to take the stereo (PCM and Dolby Digital 2.0) output via my TV's optical cable and converrt this into Dolby Digital 5.1 output using the Pro Logic II decoder.

- convert LPCM 2.0 and Dolby Digital 2.0 via optical to Dolby digital 5.1 (using Pro Logic II )
- preferably featuring optical input and output
- passthrough for Dolby Digital 5.1 tracks.

Can anyone recommend any suitable devices? Not looking for anything too expensive - preferably under £100.

So far I've found this and this, which does the same job but only featuring analogue outputs and no official Pro Logic/Dolby Digital decoding/enoding.


I've not seen anything like you are after as most people would just buy an AV receiver to upconvert stereo to 5.1 via DPL-II.
Years ago before DVD and Dolby Digital I had a Sennheiser Lucas that gave simulated surround sound to headphones, but could also output to powered 5.1 speakers. But due to its age it was only original DPL and not DPL-II/DPL-IIx etc and only had analogue inputs and outputs. IIRC at the time I paid about £400 for the Lucas with a set of good Senn. headphones, and was good at the time, but by todays standards is fairly poor performer but maybe worth a look if you can pick one up cheap enough secondhand.



Active Member
Thanks for having a look.

The lack of a digital input is a deal breaker on the Lucas, so I might just try out one of those Digital To Analogue convertors that I found - can be picked up even cheaper on eBay.

Failing that a cheap pre-amp processor for around £150 to £200 might be a better bet - just need to convert phono analogue outputs to the three 3.5mm jacks PC's use.

I'll do some more digging. Shame that there's no Pro Logic support on the z906, the speaker set peforms superbly with true 5.1 content.


Well-known Member
Hi KyoDash,

I hope you are well buddy! I agree it seems easier to get an AV receiver to do the processing for you? Would this not be suitable? How is your PC going to be connected - does it not have an optical output on your sound card.

As you probably know Prologic 2 doesn't completely convert to Dolby 5.1 - its close but you can't create something from nothing - 2 channel to 5.1 channel - it takes spatial cues from the left and right channels. ;) No where near as good as real 5.1


Active Member
I'm not actually connecting my PC to the z906 at all. Instead I'm using it as a 'budget' home cinema for my bedroom - for the TV consoles and Blu-ray.

As you probably know Prologic 2 doesn't completely convert to Dolby 5.1 - its close but you can't create something from nothing - 2 channel to 5.1 channel - it takes spatial cues from the left and right channels. No where near as good as real 5.1

Indeed, I am aware of this. The thing is Logitech's own solution makes loads of mistakes (like placing voices in 'Dolby surround' mastered films across all three front channels, and spreads frontal effects to the back), while Pro-Logic does do a reasonable job of correctly seperating the different elements in a way that feels kind of natural, if underwhelming.

The z906 does all the work of an AV reciever, so I was just looking to convert the source audio before it reaches it.


Active Member
Okay, after much searching I've found a quality device that looks like it offers some of the features I'm after - the Teufel Decoderstation 5.

I have one question though. Does anyone know if the Decoderstation 5 will convert a 2.0 PCM source via optical to 5.1 via Pro Logic?

According to the manual, the Decoderstation will convert analogue stereo sources to 5.1 while all Dolby Digital tracks are passed through unaltered. It's not clear on what it does with 'stereo' digital sources.



Well-known Member
Hi Kyodash, have you contacted the manufacturer about this? You may get your answer faster, I have never heard of this decoder, although it seems expensive for what it is. Does it mention a prologic decoder, if not you may find it alters the sound of stereo. You can get a dedicated av receiver on the forums for the price of this, with Dolby True HD, and DTS Master HD Audio. Can I ask why the reluctance to use an AVR? The Onkyos, Denons, Marantz, Sony's have more inputs than you can throw a stick at. Cheers
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Active Member
The only way to get genuine Pro-Logic decoding is by using something from a manufacturer which is licensed by Dolby and uses their algorithms. Realistically this means getting something from one of the established AV brands eg Yamaha, Denon, etc.
Anything else which claims to convert 2 channel to surround will probably end up being as disappointing as the decoder you're currently using.


Well-known Member
Couldn't agree more with MarkLG! Since manufacturers don't simply add this decoding via internal software but is generally a microchip on board that deals with the algorithms - cheap manufacturers simply can't afford the licence from Dolby to have this.

After looking at the Teufel website - it does indeed show the decoder station 5 has ProLogic II decoding, so I don't see why it wouldn't work. In order to have this feature. the manufacturer must add certain features such as PLII Movie/Music and allow you to select between Stereo, pro logic or other DSP modes. Most decoders should also at least allow PCM 2.0 as a format since most redbook CDs would be played in this format. (usually at 44.1Khz). Prologic 2 will be applied before the signal is converted into an analogue signal by the DACs. (Although I can't imagine the DACs to be that good in all fairness).

Like I said before - it should work to how you want it - but whether it is worth the extra cost will be up to you - for the price of your Logitech and Decoder station it is possible to get a really good budget seperate system (with potential for upgrade later and with THX certification).
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Active Member
Thanks for your replies, a lot of useful info which makes things clearer.

I'm not really against getting an proper AVR - that was my upgrade plan later on, pairing this with some KEF 3005 SE's when I have the budget (and re-jigged my space) to do so. The Logitech's are an extended stop-gap until I get stuff sorted.

In terms of the Logitech's, they are active speakers (powered by the sub, which also contains the onboard decoders) so I'd need an AVR with pre-outs in order to use these speakers with one - and unfortunitely this feature mainly appears on higher-end models, which are rather expensive.

It's a shame Yamaha doesn't include pre-outs on their mid-range model AVRs anymore.

In that respect, at this point in time the Decoderstation 3 might be the best option, for now. However, I agree, it does seem very expensive for what it does - especially considering that I only need it for the Pro Logic functionality (the Logitech has proper DTS and Dolby Digital decoders). Anyway, to be sure I've sent an email to Teuful to confirm if the Decoderstation 3 does indeed convert stereo PCM into multi-channel audio.

In the meantime I'll consider all of my options.


Active Member
I've been looking for something similar myself, an optical to RCA 5.1 channel converter.

I have a set of Logitech Z5300 speakers/amp which work fine with the 5.1 output from my PC which has separate RCA outputs for each channel, my PS3 on the other hand only supports 5.1 over SPDIF or HDMI both of which require some kind of decoder.

There are bunch of such things for sale on Ebay but most if not all seem to be unbranded electronics that originate in China and of the few reviews I've seen as you would expect the quality isn't good.

Shame that such a thing isn't more readily available, I don't really want to shell out again for a home cinema amp/speaker setup.

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