Is there any difference between an audio oscillator and a function generator?

[watertreader]

Hi,

Just a query. Is there any difference between an audio oscillator and a function generator? Do they merely differs in that one is used to produce waves in audio region while the other is a generic name for all wave generator?

Thanks for your help!

 

[rkodaira]

Re: Audio Oscillator

Audio generators usually have a narrower range of frequencies (including the audio band and up to 100kHz) and sine or triangle or squere waveforms.

Function generators may provide signals above 1MHz and with more features like frequency sweep, logic signals, arbitrary waveform, more waveforms (sine, square, triangle, sawtooth) etc.

Maybe there is difference in the output impedance and purity (THD) and linearity of the signals for the two instruments. Indeed I use my function generator as a audio sigmal source.

 

[neils_arm_strong]

Audio Oscillator

A signal generator can be used as a audio generator.But an audio generator cant be used as a signal generator.

 

[VVV]

Re: Audio Oscillator

Audio generators will produce a pure (low-distortion) sinewave, usually in the 10Hz-20kHz region, although some models go to much higher frequencies.
However, the distortion level is really low, since they use sinewave oscillators, mostly of the Wien bridge type. This inherently produces a sinewave when the feedback is tightly controlled, which it is. The amplitude stabilization and the time constant involved represent a disadvantage of this type of generator. When changing the frequency, the amplitude also changes and it takes time for the output amplitude to stabilize (the feedback loop time constant, which can be in the hundreds of ms).

Function generators on the other hand will generate some other type of primary waveform, triangle for example, from which all the other waveforms available from the instrument, including the sinewave, are obtained through some waveshaping circuit. Obviously, this leads to higher distortion levels on the sinewave signal, since the waveshaper only APPROXIMATES a sinewave.
Although intended mainly as a general-purpose gnenerator, a function generator can be used as an audio generator, especially if you are not testing distortion, but just the functionality of an audio chain.
The advantage of this type is that it does not require amplitude stabilization. That simply results from the thresholds of the comparator used to produce the triangle. With fixed thresholds, you get constant amplitude of the triangle wave, which results in constant amplitude of the sinewave. Thus, the feedback loop and its associated time constant does not exist, which makes this generator's output settle extremely quickly when the frequency is changed. This is the main advantage. Plus, there is the possibility of easily obtaining more than one waveform.

Modern generators actually use a DAC to output pretty much any waveform, including sinewave, and achieve low distortion levels. These are called "arbitrary waveform generators".