Clipping when recording from SPDIF input

[stevethornley]

Hello everyone

I'm new to this community and I'm banking on someone being able to help me!

I'm connecting a DAT player to the SPDIF input on my Soundblaster Live card and recording using Audacity 1.2 on Windows XP.

Within Creative Audio HQ I've got the SPDIF volume level set to 100% (for starters, perhaps someone can explain why there is a volume control when I thought this signal was staying in the digital realm?!) and when I record in Audacity the resulting material clips with high transient sounds... a piano, for example, distorts on the louder notes.

I need to take the level down to about 70% (or the equivalent in Audacity would be 0.7 - the 2 'volume' controls are 'connected') to avoid any clipping.

I've had the sound card years and used to use SoundForge without any problems. Any ideas why this is happening in Audacity?

I have downloaded the latest drivers and turned off the MOBO onboard sound in my BIOS and I have exactly the same problem in 1.3 Beta. I've also tried burning a CD just to check that the clipping is not only happening on monitoring but is actually in the sound file and it is there in the waveform. Does Audacity somehow boost the level of the signal presented at the SPDIF input of my Sound Card. And why is there an input level control anyway when I only wanted the digital signal 'untouched'.

I would be grateful for any assistance anyone can give.

Best Wishes

Steve

[kozikowski]

You can mess with digital audio way more than you think. Our commercial DAT machine, the two DigiBeta machines and the HiDef SRW deck all have the ability to move the signal levels around -- although we generally don't. It's not that hard. Multiply or divide all the sound values by some value controlled by the knob. There may be some very slight damage at each end of the digital range as you do that, but it's essentially completely lossless.

Just a note, you know that DAT and television sound are 48000, right? Not 44100. And 16-bit Stereo. Television AES/EBU and SP/DIF are very close cousins of each other. Try resetting the Audacity preferences to 48000, 16-bit, stereo and see if maybe some of the problems don't go away. Restart Audacity.

All of our commercial decks have a pre-emphasis switch and you can get into trouble with high frequencies if you have that switch in the wrong place. I've never met anybody who used it in anything.

If your recorder put pre-emphasis in and you fail to take it out, you could get very hot crisp sounds.

http://en.wikipedia.org/wiki/S/PDIF

Or your sound card could be broken or was designed to decode to analog and then digitize again.

Koz

[waxcylinder]

I had this problem a while back when I transcribed my MiniDisc recordings - I was using the SPDIF input to my USB Soundcard Edirol UA-1EX. Most of them transferred with no clipping - However there were a troublesome few that did clip. My workaround for these was to take the analog output from my MiniDisc deck and feed that to the Edirol - and then I could control the gain. Not ideal of course as the signal path went Digital=>Analog=>Digital but at least I got non-clipped recordings.

WC