Digital vs. Analog Signal Generator

[Jay]

Hi there everyone - just a quick question. We are using the Wavelab
program to digitally generate a sine wave. Is there any
advantage/disadvantage to using a digitally-generated signal as
opposed to if we used an old 1960's style signal generator? Is it more
noisy, necessarily? This is for a science project.

Thanks!
- J

 

[Tim Wescott]

Hi there everyone - just a quick question. We are using the Wavelab
program to digitally generate a sine wave. Is there any
advantage/disadvantage to using a digitally-generated signal as
opposed to if we used an old 1960's style signal generator? Is it more
noisy, necessarily? This is for a science project.

Thanks!
- J

Digital is more accurate, and for an affordable signal generator it's
probably cleaner. These days only a purpose-built high-end analog
oscillator will be better than digital. I wouldn't expect an analog signal
generator to do better than digital unless it uses a true sine-wave
oscillator (assuming you're doing this in the audio range).

But tubes are more fun, so go with the '60s style.

 

[Paul Burridge]

Digital is more accurate, and for an affordable signal generator it's
probably cleaner. These days only a purpose-built high-end analog
oscillator will be better than digital. I wouldn't expect an analog signal
generator to do better than digital unless it uses a true sine-wave
oscillator (assuming you're doing this in the audio range).

But tubes are more fun, so go with the '60s style.

He hasn't stated a frequency range so this is a bit of an assumption.
There are some rather good ULF oscillators using FET-based active
devices; the digital equivalent will have the drawback of quantisation
noise.

 

[Tim Wescott]

He hasn't stated a frequency range so this is a bit of an assumption.
There are some rather good ULF oscillators using FET-based active
devices; the digital equivalent will have the drawback of quantisation
noise.

That would meet my definition of "purpose-built high-end". Then again,
_anything_ that threatens to win the argument would meet that definition
. Also, the lower the frequency the more bits you can economically cram
into your DAC, so the better the Q noise.

It really depends on how much money, patience, and experience you have. I
would expect that the only modern really professional signal sources that
aren't digital are going to be very high frequency or very narrowly
targeted. If you need a good signal, have no money but do have time and
experience then an older signal generator is definitely the way to go. If
16 bits is enough and you're working in the audio range, then digital is
probably for you. Same with 12 bits and HF -- get a DDS and have fun.

 

[Jim Yanik]

[email protected] (Jay) wrote in

Hi there everyone - just a quick question. We are using the Wavelab
program to digitally generate a sine wave. Is there any
advantage/disadvantage to using a digitally-generated signal as
opposed to if we used an old 1960's style signal generator? Is it more
noisy, necessarily? This is for a science project.

Thanks!
- J

It all depends on the specifications of the individual generators.
Noise and harmonic distortion. RTFM's.
Or you could compare on a spectrum analyzer.

Digital generators will generally have a more stable frequency.