I want to play audio out of the headphone jack on our HP laptop.

I want to play audio out of an 8 channel sound desk and i am using a 3.5mm to 3.5mm lead with a 3.5mm to 1/4 inch adapter on one end to link the two.

Sometimes it plays sounding scrambled, sometimes it plays fine, sometimes it plays elements of the audio track (like the music) but not some of the voices if I'm playing a video.

The sound plays fine through headphones.

This is really baffling me. Any ideas?

If you want more details, please ask.

You don't say exactly how (where) you are connecting the audio into your mixer, but if you are using a 3.5mm to 1/4 inch adapter, it seems like you are using some sort of monaural line-level input. Knowing exactly WHERE you are connecting to your sound desk (and what make/model) would be helpful.

However, even without those details, it seems quite probable that you are taking the unbalanced stereo output from your laptop headphone jack and sending it into a balanced monaural input. In the best case, you might get just the left channel, but you are more likely to get the two stereo signals subtracted from each other, giving you a very wierd signal.

The solution is simply to use a proper "stereo-breakout" cable where the left and right signals from your laptop are delivered to separate plugs for your desk. For example...

Stereo Breakout - Hosa Technology (http://hosatech.com/product/cmp-150/)

I can't get those details for you right now but I'll be using the desk on Tuesday night so if necessary, I can get them then.

The inputs that the desk has are XLR and single 1/4 inch jack inputs.

I have ordered one of the cables you mentioned but the desk does not accept stereo inputs. Would an 3.5 to XLR lead provide stereo sound?

3.5 3.5mm Jack to XLR Male Speaker Mixer Cable 2m Gold | eBay (http://www.ebay.co.uk/itm/3-5-3-5mm-Jack-to-XLR-Male-Speaker-Mixer-Cable-2m-Gold-/250451408282?pt=LH_DefaultDomain_3&hash=item3a5011359a)

Mixers typically do not accept stereo inputs.
The left channel of stereo and the right channel of stereo are two separate separate audio signals. You would connect the left channel to one of the inputs of the mixer, and the right channel to another input. Then, you can pan the left signal to the left and the right signal to the right (if you are creating a stereo mix).

No, that 3.5mm to XLR cable would not be suitable.
1) You are still connecting a STEREO source into a MONO input. Same problem you are already having.
2) You will be connecting a headphone/line-level signal into a mic-level input. The audio will be very distorted because the mic input can't handle that signal level. It will probably be worse than what you are doing now.

Ah interesting. That makes a lot of sense. Thank you.

Most pro and semi-pro mixers have balanced line level channel inputs via a 1/4" TRS connection. Plugging in a stereo source via TRS plugs sends audio to both the tip and ring connection.. which are 180 degrees out-of-phase, so center panned mono sources will cancel out altogether or partially (while others may sound louder), depending on the mix.
Get a proper cable as Mr. C. suggested.
In addition, many computer HP (headphone) outputs need to be run through a transformer for optimum quality. Investing in a direct interface box (DI) would be wise. The $25-30 Rolls DB25 is an affordable consideration, and would combine the two (stereo) channels effectively. However one would still need the 3.5mm stereo to dual !/4" adapter cable..