clipping at +/- 0.5

[simon lees]

When recording, the clipping happens at +/- 0.5 on the wave screen whereas I thought it shoud lhappen at +/- 1.0. Why is this and what can I do about it?

[steve]

It all depends on where the clipping occurs.
Audacity will clip at +/- 1.0, but your microphone, pre-amp, sound card, (whatever is in your signal chain) will have its own clip level. Try fiddling with the levels at each point in the signal chain and see if you can find where the clipping is occuring. (A very common reason is when people feed a "headphone output" into a "mic input" and overload the "mic in").

[simon lees]

My input is coming from a mixing desk and goes via the inline socket. The inline volume is set to max so that I can adjust the sound in via the mixing desk. Not sure where to look for setting the clipping levels for the mixing desk or the sound card.

[steve]

What sort of mixing desk do you have?

[simon lees]

Steve HI,

It is a Soundcraft Spirit LX7. If that helps.

[kozikowski]

<<<goes via the inline socket.>>>

On your Windows Laptop? Those machines tend to not have Line-In in favor of Mic-In which like to overload pretty much exactly like you're describing. Roughly a thousand to one mismatch in sound level.

Koz

[steve]

That's fine, I just needed to know what features you have available on the desk.

For each input that you are using, check the "pre-fade level" (PFL). There will be a button near the fader of each channel for selecting PFL (consult your manual if you can't find it - this is one of the most important functions, so you need to know how to do it).

The Pre-Fade Level should meter reasonably high, but should never go into the red. Adjust the gain (sometimes called "trim") as necessary. Note that if you adjust the channel Eq you will need to recheck the PFL.

If you are using Aux send/returns, you should check the levels of these also.

When you are satisfied that these are all correct, return the metering back to the stereo mix and gradually turn up the faders. If you are using a line input on your computer you should see a reasonably high level on the mixing desk meter as the record level meters in Audacity show a good level. You will not necessarily have both sets of meters showing the same levels as there is more than one definition of "Line Level". Professional audio equipment usually uses a higher signal level than domestic audio equipment, so the level on the mixing desk may appear to be a bit low.

If you need to turn the mixer master level so low that it does not show on the mixing desk meter at all, then you are probably using a microphone input on the computer instead of a line level input (that will not work - you must use a line level input).

The level on the mixing desk should never go into the red.

The recording volume for the computer should be set using your sound cards control panel/mixer (or the Windows Mixer). Do not rely on Audacity to control the recording volume.

Some sound cards are designed to work best with the recording level set to around 70 - 80%, other sound cards work best with it set to 100%. You will probably need to experiment as this does not usually get mentioned in the sound card documentation.

Note that there are often 2 controls for the sound card record level. There is the "line in" level, and then there is the "master record" level.

Check that you have selected "Line in" as your recording source and not "Stereo Mix". (in the sound card control panel/mixer).

You have not mentioned what is plugged into the mixer. Are you recording from microphones? Are you sure that the distortion is not occuring before the mixing desk?

[steve]

<<<goes via the inline socket.>>>

On your Windows Laptop? Those machines tend to not have Line-In in favor of Mic-In which like to overload pretty much exactly like you're describing. Roughly a thousand to one mismatch in sound level.

Koz

Some PC laptops claim to have inputs that can switch between mic level and line level, but they are still usually rubbish and likely to cause problems. Making good quality recordings on a laptop invariably requires either an external sound card or a Mac.

[simon lees]

A bit more info. I am using a desktop and line-in is selected for the sound card which is a Realtek.
The clippings happen at exactly +/- ).5, so exactly half of the normal +/- 1.0 so I cannot see it is a question of adjusting levels somewhere, more that some setting needs to change.
I have Audacity set at sample rate 22,050 and it is taking a mono signal. The sample format is 32-bit. I notice that the settings on the Realtek are 44,100 and 16-bit. Does this have an infulence?

[steve]

I am using a desktop

That's good - it means that you have more available options.

The clippings happen at exactly +/- ).5, so exactly half of the normal +/- 1.0 so I cannot see it is a question of adjusting levels somewhere, more that some setting needs to change.

"adjusting levels" vs. "change some settings" - that's a bit of a fine distinction

If the sound is being clipped, then it is because something somewhere is being overloaded. What we need to do is to find out what is being overloaded. We can then look at why it is being overloaded and hopefully determine if it is due to a "user setting" (I'm including the concepts of buttons, sliders, switches, check boxes, and all other forms of user interaction), or whether it is due to a hardware fault (something that will need repairing or replacing).

I presume that you have checked everything already mentioned.

I also assume that the clipping is causing audible distortion when you play back the recording.

If you plug headphones into the mixing desk and listen to the main mix, does it sound OK (clear and absent of clipping)?

If so, then either;
1) Your sound card is faulty (or just very poor) and needs replacing.
2) You have the output from the mixing desk too high for the input of the sound card to handle.
3) You need to adjust the record levels in the sound card control panel/mixer.
4) The sound card drivers are faulty and need upgrading.

My money is on No.1, but it's worth checking out the other options before buying a new sound card.

RealTek sound cards are usually "on-board" sound cards and are not really designed for recording. They will usually work well enough for making computer beeps and pings, for internet phone calls, and for playing MP3's through little computer speakers, but not for much else. Since you have a nice mixer, I guess you are quite serious about making some good recordings, in which case a nice sound card will definitely be money well spent. You should look at sound cards that are designed for music/recording rather than game cards. The cheapest option is probably the Behringer UCA 202 (a USB line level in/out device) which is designed as a cost effective interface for line level devices such as mixing desks, CD players, tape decks, etc.