iMac works at 44.1kHz not 48

Hi,

The only problem I see in your setup relates to how you have the "sync" set up.

When syncing to an external digital device, the clock source should be set to "External".

Even though you are getting signal input at 44.1 it may be because the clocks are very close and they lock or it may be the Mac's audio clock is native to 44.1.

When syncing to digital devices there can only be one digital clock master, in this case it has to be the DAT, so..give it a try with the Audio/MIDI Setup set to External Clock.

If this doesn't work are you sure the coaxial -> optical convetor supports 48k

pancenter-

Ok,

I have an older G5 tower with an optical input so what I see may be different.

Go to Audio/MIDI setup under Audio.

On the left side default input should say built-in audio (at least that's what I have.

Underneath that you should have properties for built-in audio.

Further below that it should say..

Audio Input:

Source:

What do you have listed under the Source... I have "Line-In and Digital-In"

You may have Digital In or Optical In?

Let's get that far.

pancenter-

Ahhh... ok, sorry, our systems are indeed very different, the iMac you have is setup to auto sync to an incoming digital signal. Not sure why 48k is not recognized.

You might try unplugging the digital input, start the DAT playing at 48k then plugging the digital input back in, this might force a switch. Also, if you're using a plain old coaxial audio cable try a different one.

Another way might be to open an audio editor and switch the internal sample rate to 48k, then plug the DAT in with a 48k tape playing.

In Audio/MIDI set the internal sample rate to 48k, (think you've done that).

Playing a DVD will also cause the internal sample rate to switch.

Hopefully it's not a limitation of the convertor, doesn't seem like it should be.

pancenter-

p.s. is the convertor bi-directional.. in this case you only want to have the DAT OUT to the Mac IN.

It might be worth a few bucks to purchase a 3-ft (preferable) or 6-ft cable made for digital audio, they have a slightly different resistance than a standard audio cable, but there's no guarantee. I've used audio cables like the one you described with no problems.

Know anyone else that could try the convertor to make sure it will do 48k?

pancenter-

The only other settings related to "Sound" are in "System Preferences" but I don't think you'll find anything there.

Is the tape recorded at 48k a commercial tape or could it be encoded with a digital copy protection scheme.

Does the DAT machine have a SCMS switch?

Of course, you can always go analog.

Your other option is a USB or Firewire audio card that has a digital input

pancenter-

I noticed there a various problems using digital I/O on recent Macs, see the "More Like This" sidebar.

pancenter-

Julia12341234 wrote:

I've gotten it to "work" on and off with 48K with a high end coaxial cable. When it does see the signal, it has popcorn static in it. 44.1 is fine with the new cable. This problem is in either software program and direct in and out of the Mac with no other software involved. . I exchanged the converter for a new replalcement, same problem. THe only thing not replaced is the optical cable, which is brand new and has a steady red light through it. Could the Mac input be faulty at 48 but not 44.1?

The popcorn static is a symptom of poor digital sync...

It's possible the Mac's hardware is simply not good enough to sync at the higher sample rate while at the same time have no problems playing back 48k audio or even higher sample rates. Both iMacs and Laptops pack a lot of circuitry into a small physical space, the (electronic) noise level from all the minature circuitry affects audio input and output. The noise floor of the analog inputs is very poor, sometimes as bad as -50 to -60db.

So, it's possible the digital input can't get a clean enough signal at the higher rates... or, it could be the s/pdif converter. Difficult to say.

Are both the iMac and the DAT plugged into the same power outlet, it helps keep down ground loop noise if every thing is running off the same power strip.

pancenter-