# Laptop Sound Calibration graph



## TheWoat (Sep 22, 2008)

Hello, 
I just ran REW to check my laptop built in sound input. I turned off all enhancements and selected the highest sampling rates (24 bit 192kHz 2ch) and got the graph below. It seems adequate enough to hook up an SPL meter or a mic+preamp, any thoughts?


http://img109.imageshack.us/img109/1771/laptopsoundcard.jpg


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## brucek (Apr 11, 2006)

> any thoughts?


You had a meter/mic calibration file loaded when you ran that soundcard calibration routine. The telltale is that soundcards don't have more output at the extremes - they drop off their response at their extremes.

Rerun the routine with the meter/mic file cleared. Also set the sampling rate to 48Khz.

I trust your laptop has a proper line-in and you're not using a mic-in?

brucek


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## TheWoat (Sep 22, 2008)

Looking at the options for audio recording, it says "External Mic". I have a couple desktop computers with Line In, but I was just seeing if my only laptop usable for this sort of thing.

I reran it with that box unchecked, now it is dead flat. I realize I have a Mic-In, but if it can handle the full audio range, what other things should I check to make sure it is an appropriate sound card to use with REW?

Edit, I reran it again at the correct volume level... 








http://img130.imageshack.us/img130/1771/laptopsoundcard.jpg


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## glaufman (Nov 25, 2007)

TheWoat said:


> Looking at the options for audio recording, it says "External Mic". I have a couple desktop computers with Line In, but I was just seeing if my only laptop usable for this sort of thing.
> 
> I reran it with that box unchecked, now it is dead flat. I realize I have a Mic-In, but if it can handle the full audio range, what other things should I check to make sure it is an appropriate sound card to use with REW?
> 
> ...


I think the operative questions are:
Is it designed as a line in or as a mic in?
If mic in, does it have a preamp?
If so, is that preamp acceptable (as most are not)?

I have to admit that (to me at least) the plot looks reasonable... I might be inclined to say proceed (but with caution)... 

Let's see what others say...


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## brucek (Apr 11, 2006)

SPL meters (such as the Radio Shack meter) output a line-level voltage signal. The standard microphone input jack of a laptop offers high gain since actual microphone signals are quite low in relation to a line level signal.

This extra gain at the mic inputs front end usually results in increased noise.

Mic inputs usually enjoy a very limited bandwidth that is designed to comply with a narrow voice frequency range that a cheap microphone would supply. The port often supplies a 5 volts bias signal for cheap computer mics.

In this case it looks like the bandwidth is quite adequate, so it may indeed be a line-in jack - this would have to be verified in your laptops specifications.

Most members that use laptops for REW purchase an external USB soundcard. They are quite inexpensive and offer line-in and line-out suitable for REW.

brucek


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## TheWoat (Sep 22, 2008)

Thanks for the response. I have a couple desktop computers as backups with line-ins, and Ill drag them out of storage soon and compare graphs, possibly noise as well.

During the test, I did "clip" the input until I got the sound levels low enough and figured things out a little... and it still works, I would hope there is some decent circuit protection at that input. Funny how desperate I am to save $30 bucks. Thanks again.


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