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Old 19th July 2002, 05:16 AM   #1
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Default Poor man's signal generator.

One of the things I haven't got at home is a signal generator so what I usually do it generate waveforms on my computer and feed them out the sound card. The quality and especially the frequency response and noise floor is not that good, so I was thinking I might generate a number of waveforms using Cool Edit or similar and burn them to an audio CD as separate tracks, and then play them using the CD player's much cleaner output.

I am looking for suggestions as to what I might put on this CD, the kind of things people use for standard tests of one kind or another.

GP.
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Old 19th July 2002, 05:23 AM   #2
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You'll need 1khz (and several multiples) sines and squarewaves, and perhaps pink & white noise too which might come in handy. I'd still reccomend a small signal generator; Rod Elliot published one recently that seems very good ( www.sound.westhost.com , search for the MiniOsc).
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Old 19th July 2002, 06:21 AM   #3
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As I suggested on another post, why don't you just buy an audio oscillator or function generator?
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Old 19th July 2002, 06:43 AM   #4
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Default Re: Poor man's signal generator.

Quote:
Originally posted by Circlotron
I am looking for suggestions as to what I might put on this CD, the kind of things people use for standard tests of one kind or another.
Might be easier just to order one of the Bass Zone CDs from John at Stryke. I found this quite useful until i started using the software wave generator that comes with Mac-the-Scope which i have been using on my PowerBook -- for my purposes so far it hasn't had any noise problems.

Click the image to open in full size.

dave
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Old 19th July 2002, 11:44 AM   #5
yeti is offline yeti  Germany
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There is another possibility, get a Wave Editor program many of them have funktions to generate sine waves, FM Signals, and Wobbulator signals.Save them to .wav format and burn it to a CD.
Now you can use a portable CD player as a precision Audio Generator.
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Old 19th July 2002, 01:13 PM   #6
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Now why didn't *I* think of that?

GP.
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Old 19th July 2002, 03:10 PM   #7
alvaius is offline alvaius  Canada
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Either buy an audio card with an SPDIF output or get an SPDIF add on, they are pretty cheap. You can then run right into a receiver and use the DACS in it. That gives pretty good quality.

I use a Soundblaster Extigy. I find it is quite good. The basic Soundblast Audigy is down in the $60-$70 range if you look. It has pretty good quality.

Alvaius
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Old 19th July 2002, 03:50 PM   #8
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Default What good is a sound card sig gen?

What is the "utility" of a sound card signal generator if it's in an environment (your PC) abounding with EMI, if it doesn't have a precise load or attenuation system, if you can't be certain of it's output over a 3 decade span of frequencies?

A precision, stable, low THD sine generator can be built for less than $30, a Heathkit IG18 can be retrofitted for distortion levels less than 0.01% for less than $20 and the IG18 is about the size of a shoebox. You can make a wobulator with a pair of XR2206's -- and it will fit in the palm of your hand.
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Old 19th July 2002, 04:48 PM   #9
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Default Gunna

Hi Graham,
Some usefull test tones on test cds that I have used are tracks like digital silence and tones at 0dB and reducing in 10 dB steps down to very low level (-80dB etc) - these can reveal some pretty shockingly yukk spurii (digital, servo and psu induced) coming out the end of a system.
In my experience the RF (out of audio range) junk emitting from a DA stage can cause all sorts of mostly imd and signal reflection problems downstream.
How well the complete amp input/amp output/cable/louspeaker/room chain behaves electrically (handles the whole thing) when fed this in band and out of band noise junk is critical in our now digital age, and is the maker or breaker for long term enjoyment - an electrically correct sytem sounds correct.

When I make my own test disc (gunna) I will include extras like ascending or descending sawtooth tone and rectangular pulses for verifying system polarities, two and more tone type IMD tone sets, and white/pink noise.
Also musical passages that have been filtered (LP, BP, HP) with different types and slopes.
Also usefull would be short grabs of particular musical passages looped many times for purpose of 'on the fly' component A/B sonics testing - an UN earthed solder tip is mandatory for this.
Also the same looped musical passage grabs recorded with alternating polarity.
Also natural sound recordings of places that you are familiar with - eg your back yard or family members recorded in alternating polarity.
Also a short announcement track (PC generated voice or natural voice) before each test track.
Magix Samplitude Producer 2496 v6.0 (15 Mb) 90 day trial is a very good audio editor and has all sorts of in built effects and a signal generator giving all the above signals.
ps - I just downloaded 'Samplitude Master' and it seems the same.
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Old 19th July 2002, 05:06 PM   #10
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<b>I agree with jackinnj but . .</b>
<blockquote>
There are plenty of audio oscillators available on ebay. I picked up a Hewlett Packard 204C for less than $50. Millivolt meters, function generators and scopes also abound.
</blockquote>
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