clipping-top of one channel only

[erblaser]

I have been using CD Doctor from an old version of Toast (5.1) to digitize my old records via the i-Mic pre-amp. This version of CD Doctor seems to work OK, but the other Toast features all crash so I recently started using Audacity to combine sides 1 and 2 of the records and to remove noise.

However, when I open these .aiff files with Audacity, the top channel in the display looks fine, but the bottom channel is clipped at the 0.5 level, but not at the -0.5 level. The top channel exhibits no clipping.

In CD doctor the same .aiff file shows no evidence of clipping in the display, so it doesn't appear to have anything to do with the recording, but rather opening the file in Audacity.

Any ideas if this is a real clipping? I can't tell by listening to the audio, at least not with this kind of music. Or is this asymmetric clipping of only one channel real, and if so, is there a fix? Perhaps I accidentally activated a feature without realizing during my exploratory activities.

I am doing this with an i-Mac running OS 10.6.8 and the most recent version of Audacity, i.e., 1.3.14-beta (Unicode).

Ed B

[kozikowski]

I don't have a terrifically high opinion of the iMic. You do have it switched to LINE right? The device is intended to amplify a "Computer Microphone" so the computer can use it. The Stereo Line-In is an afterthought. It doesn't have a Phono-In, does it?

Any reason you're not using the high quality encoder inside your iMac?

For example:
http://kozco.com/tech/audacity/pix/MacLine-In.jpg

Koz

[erblaser]

The i-Mic seems to work fine with CD Doctor. It has two input levels, one that works directly off of a turntable, and one that works with my old reel-to-reel tape deck.

I can't vouch for the quality of the signal the i-Mic/CD Doctor conversion is producing, but right now I am more concerned about why I would get this strange asymmetric clipping of the signal on one channel with Audacity, while the signal looks fine on CD Doctor. I would prefer to use Audacity since it is so much more powerful than CD Doctor, but I don't want to start converting my records using Audacity if the resulting digitized files are going to have this funky problem.

Thanks.

Ed

[kozikowski]

Do two screen captures and post them using "Upload Attachment" under the forum text screen. One with a song from CD Doctor and the other, the same song in Audacity illustrating the damage.

You could also Export a small portion of the damaged sound as FLAC and post that on the forum, too. You probably won't make it much past about five or six seconds, so you won't be posting an album.

Koz

[erblaser]

I have attached the .aiff files from Audacity and CD Doctor for comparison.

Ed

[steve]

I think that it is more likely that the display in Audacity is correct.
The waveform in CD Spin Doctor appears to be identical for both left and right channels which would be surprising unless the original recorded audio was mono. I suspect that CD Spin Doctor is creating the waveform display from an analysis of only the left (upper) channel.

Could you upload the .aiff file somewhere (for example sendspace.com) and post a link so that we can examine the file.

[erblaser]

The record whose attachments I sent before is actually a monaural record that was enhanced for stereo, which probably means they just duplicated the monaural channel. Hence the two channels are identical.

The attachments to this post are from a more recent record which I hope is stereo. It's singing, so there isn't that much difference between the two channels, but they do not look identical to me.

Let me know if you still want me to upload files to sendspace, or if this post is adequate. If the former, let me know if you want an entire record or just one or two tracks of the record.

Thanks.

Ed

[steve]

Let me know if you still want me to upload files to sendspace,

Yes please.
I don't need the whole project, just a short sample in WAV or AIFF format that demonstrates the problem will be sufficient.

[kozikowski]

If you mess something up in the encoder (iMic) the right channel is the one to take the hit. I, too, believe the Audacity version.

What's the iMic version or model number?

Koz

[kozikowski]

This one?
http://store.griffintechnology.com/imic

You're not using it like it was intended to be used. The Line-In is for a stereo CD, Cassette Player or music mixer. The other connection is for a "computer microphone" like this...

http://www.kozco.com/tech/audacity/pix/PCHeadset.jpg

The iMic doesn't have a phono preamp and you can get into trouble trying to digitize a turntable directly. The proper device is something like this...

http://www.behringer.com/EN/Products/UFO202.aspx

With the input switched to Line for the reel to reel and Phono for the turntable.

You are using a straight turntable?

http://en.wikipedia.org/wiki/Technics_SL-1200

and not a "USB Turntable"...

http://www.ionaudio.com/products/details/profile-lp
http://www.bestbuy.com/site/Ion+Audio+- ... Id=9473321

Koz