iMac Line in connection

[Roland Gama]

Has anyone been successful using REW with the 17"imac?
Though it has a line-in at the rear it supports only "sound studio" software.
Hope there are some imac users out there?

[mrsollars]

i'm in the exact same boat......but a 24'' imac.

thanks
matt

[JohnM]

Can't think of a reason it shouldn't work. As long as you can select the line in and line/speaker out as the defaults in the Mac's system audio settings REW should be able to use them.

[Roland Gama]

Hello John,
Tried for some time yesterday with the audio settings of the imac. All it says is that line out is not supported. I had faced this problem about a year back when I tried to get the TV audio signals in the imac and use it to feed a small 5.1 system.((Although the itunes, etc worked well.)
I phoned apple for support.
Reply: The line in works only if used with a software like "Sound Studio"
I installed sound studio and it worked but I could not use any controls of itunes eg. equalizer.
Sound Studio has a tab which you can tick and it sends the line in signal to line out straight through.

So yesterday as I said I tried using REW with sound studio support.
It works in as much as accepting the spl meter signals and spl calibration.
The rest does not work.ie. The sound card cant be calibrated.(It shows a very large dip below 100 Hertz.) The left channel cant be looped back.
The sweep works with all its function filters etc. However, accuracy is questionable.

Secondly I decided to purchase the DEQ2496 to use with REW. I found a calculator to convert BW to Q. Here is the link.http://www.sengpielaudio.com/calculator-bandwidth.htm
What do you think about it John?

[Roland Gama]

Need further investigation on Griffin's iMic. It should work as you can set the line-in and line-out in the audio preferences.

[JohnM]

Regarding the calculator, unfortunately Behringer are rather inconsistent in their definitions of bandwidth, y0u would need to connect the unit in a loopback and measure some filters at various bandwidth settings to see whether the DEQ corresponds to the FBQ2496 definitions, the DSP1124P or something else.

[Stretch]

Hi Roland,

I have a recent model iMac and will be starting to play around with REW soon. I'll let you know if I can figure out what the problem is. Have you tried using Apple's own GarageBand recording application which is bundled with most Macs?

Another possibility might be a free software program (we like those!) called Line-In which allows direct playthru from your input.

For reference, here are the stated specifications of the iMac's analog audio input/outputs. I believe they are the same as all other Macs, so there shouldn't be any model-specific limitation as far as I can see.

Line input

The analog line input operates independently from all other audio input ports and is always available. The line input supports recording at bit depths of 16, 20, or 24 bits per sample and at sample rates of 44.1 kHz, 48 kHz, or 96 kHz. Audio recorded from the line input is presented as a stereo data stream. The line input gain can be adjusted from -16 dB to +30 dB.

During input of a 1 kHz, 1 VRMS (-3 dBFS) sine wave (44.1 kHz input sample rate, 24-bit sample depth, 0.0 dB input gain, no weighting) the audio line input has the following nominal specifications:

Jack type: 3.5 mm (1/8-inch) stereo
Maximum input voltage: 3 VRMS (+11.8 dBu)
Minimum voltage input for full scale output: 63 mVRMS (-21.5 dBu) at input gain = +30 dB
Input impedance: > 20 kilohm
Frequency response: 20 Hz to 20 kHz, +0.5 dB/-3 dB
Signal-to-noise ratio (SNR): >90 dB
Total harmonic distortion + noise (THD+N): <-85 dB (0.006%)
Channel separation: > 85 dB

Line/Headphone output

The headphone output is automatically selected for audio output if no external S/PDIF optical digital output device is detected. The headphone output supports a stereo data stream at bit depths of 16, 20, or 24 bits per sample and at sample rates of 44.1 kHz, 48 kHz, or 96 kHz. The headphone output volume can be adjusted from 0.0 dB to -64 dB.

During playback of a 1 kHz sine wave at -3 dBFS voltage level, 24-bit sample depth, 44.1 kHz output sample rate, 100 k load (unless otherwise specified) the audio output has the following nominal specifications:

Jack type: 3.5 mm (1/8-inch) stereo combo
Maximum output voltage: 1.6 VRMS (+6.3 dBu)
Output impedance: <24 ohms
Frequency response: 20 Hz to 20 kHz, +0.5 dB/-3 dB
Signal-to-noise ratio (SNR): >90 dB
Total harmonic distortion + noise (THD+N): <-80 dB (0.007%)
Channel separation: >85 dB

[Roland Gama]

Thanks Stretch.
The information is comprehensive. I have already downloaded Line-in and will give it a try.
Very few mac users this side of the globe-probably less than 1%. this too being very optimistic.

Do let us know how you progress.

[Roland Gama]

Hello Stretch!!!

The Line- in free software worked. I sucessfully calibrated the imac's sound card. Flat as a straight line.
Feeling happy with the great achievement.Thanks a lot mate for saving my time and money had I purchased the "imic".
Will do some measuring tomorrow.

[Stretch]

Happy I could help. And thanks for saving me from banging my own head against the wall over this! Please let me know how you get on. Judging by previous posts, there's been some frustration from Mac users trying to get REW up and running, so if we can figure it out I'll write up a short primer and maybe the mods can sticky it for posterity.

PS: Are you running Leopard, or an earlier version of OS X? Apple just recently added support for Java SE 6, which may help matters. I seem to recall JohnM mentioning there were some issues with Midi communication on the Mac under SE 5.

[Stretch]

Also, could you possibly post your calibration graph, Roland? I spent a half hour today fiddling with the Audio Midi on the iMac and could not get a decent measurement, as you can see below.



I then hooked up an external audio interface I have with far better results.



So I'm very curious how you got the iMac's onboard audio set up in the end.

Thanks.

[Stretch]

Well I'll be a monkey's uncle. Came back, reset everything to defaults and immediately got a clean measurement on the internal sound card without using the Line-In application. iMac is in red vs. external interface in black. Pleased, but puzzled.



At any rate, here are the iMac audio settings that worked for me.

Input:



Output:



Time for a beer, I think.

[Roland Gama]

Hello Stretch,
Some of my observation with REW are as follows:
When REW does not respond as you expect it to then quit it and restart.
The comb filter like reading you have in the soundcard calibration is because you set the speed higher than 44.1Khz. John has mentioned this somewhere about macs.
The Line in freeware is always working unless you uninstall it.
Your last graph with the soundcard is similar to mine except than mine has greater peaks and dips before 20khz.
I feel you are in the right track. Have you done a soundcard calibration file?
(By the way, I am neither a computer geek nor an audio engineer but a dentist.)
I have printed the whole lot of help files and keep reading it during my spare time.
Yesterday I got to Impulse response.

[Roland Gama]

Yes I am running leopard. Will check the java SE6.
Thanks!