Audio Generator or Function Generator? - Page 1
Forum section: electronics / testgear

author: riverrat373
author_rank: Contributor
timestamp: January 01, 2015, 08:25:22 pm
content: Hello! I just joined the forum and hope to learn more about DIY electronics from members here. I have a project coming up that requires an audio generator and I'm confused about the different generators available. Can I substitute a function generator or a signal generator for an audio generator? Will they produce an audible signal that I assume the audio generator does? Would they be more versatile? Will I eventually need all three as I progress in my skills or will one serve as all three? Any guidance would be greatly appreciated!

author: KD0RC
author_rank: Regular Contributor
timestamp: January 01, 2015, 08:34:28 pm
content: Generally, any that you mention will generate audio signals. They tend to go up in price (with some exceptions, of course) in the order:Audio Generator (many are free - they use the sound card of your computer)Function GeneratorRF Signal GeneratorMy suggestion would be to start with an audio generator, get some experience, and then upgrade only if you need to.Len

author: riverrat373
author_rank: Contributor
timestamp: January 01, 2015, 08:45:58 pm
content: Quote from: KD0RC on January 01, 2015, 08:34:28 pmThanks for the reply! I understand what you're saying, but I'm retired and on a tight budget with all my hobbies I have so I would like to make just one investment if possible. I have been watching the local Craigslist for the last month and nothing has come up there. I am reluctant to buy used equipment from Ebay because I have been burned before and I hate all the trouble it is to get a refund out of a reluctant seller! (IE--"I powered it on but don't know how, or have the equipment to fully test it but it should work OK. No refunds given.") You know what I mean?

author: jpb
author_rank: Super Contributor
timestamp: January 01, 2015, 09:29:06 pm
content: Specialist audio generators can have better distortion figures than more general function generators and some old ones are very cheap (if rather bulky).Krohn Hite are a good name and I've seen them from time to time at low prices (and also at very high prices e.g I almost bought one for £50 before deciding it was too bulky but at the same time some sellers ask hundreds of pounds/dollars).

author: SkyMaster
author_rank: Frequent Contributor
timestamp: January 02, 2015, 05:14:44 am
content: Typically, an Audio Generator has an internal oscillator that generate a sinewave. This sinewave can be very close to a pure sinewave (very low distortion; less than 1%).Audio Generators output Sinewave and sometime also Squarewave.Almost all (if not all) analog Function Generator generates, internally, a triangle waveform, then this waveform is going through a "sine shaper" circuit. The end result is a sinewave which is not a pure sinewave, its distortion is higher; typically 2% to 3%.Function Generators output Triangle, Sine and Square waveforms.

author: Marc M.
author_rank: Regular Contributor
timestamp: January 02, 2015, 06:04:10 am
content: As others have pointed out, Audio generators are designed to have very low distortions down to well under 1%. But because they are designed for audio work, they are limited in frequency range, waveform types, etc.Function generators are designed to have a wide variety of output waveforms many including ramps and pulses in addition to the standard sine, square, triangle. They also have very wide frequency ranges, with modern FG running from mHz to several hundred MHz. Many offer additional features such as sweeping a range of frequencies and the ability to modulate the base frequency. This makes a function generator many times more useful.Therefore, unless you specifically need very low distortion audio signals for your project, you want to pick up a function generator. Regarding purchasing off Fleabay, I've had very few issues. A lot of the equipment I purchase is listed as not working, but more often than not it works fine after doing basic maintenance such as cleaning control pots, switches, etc. I've also had very good luck in getting some money kicked back when it's advertised as "working good" and I run into problems after receiving the item. I have over 500 purchases on Fleabay, a lot of it is electronics related, and I've only had a couple of issues (one on a guitar and one for a universal remote) and just recently on the bogus Fluke meters for $13.00. In every case I got my money back though I had to jump thru a lot of hoops on the remote. Where I live in the middle of Iowa I would likely die before I ever found any decent T/M equipment at a reasonable price on Craigslist. I think Fleabay is one of the best places to pick up T/M gear despite the occasional issue.

author: jpb
author_rank: Super Contributor
timestamp: January 02, 2015, 11:37:42 am
content: Quote from: Marc M. on January 02, 2015, 06:04:10 amI would second this, but add that you need to be careful. I'm amazed at some of the prices sellers ask - there are some sellers that just add a large mark-up to catalogue items from companies like Farnell yet at other times you can find a bargain. Even within one seller's shop (eg Agilent/Keysight/HP/Whatever store) where some items with multiple options are sold at a low price whilst others seem near-to-new cost.Cheaper bargains tend to be sold by those who don't know what they are selling. The cheap Krohn Hite oscillator I almost bought I found by just searching on the keyword "oscillator" rather than "audio oscillator". It was amongst general stuff from a clear out and the description was based on what was actually labelled on it. This compares with dealers in used equipment who seem to ask very high prices and just keep listing for months/years until someone comes along who is willing to pay (and probably later regrets doing so!)So I'd suggest searching on multiple things like "oscillator", "audio generator", "function generator","frequency source" etc though it might be a bit tedious looking through all the irrelevant stuff.

author: larry42
author_rank: Regular Contributor
timestamp: January 02, 2015, 12:07:44 pm
content: To the OP.If funds are limited, and you only need audio frequencies - then use a computer soundcard. Preferably external, and perhaps get an audio isolation transformer to prevent damage to the computer in case of grounding mistakes. I believe there are a bunch of programs out there that will give you Audio Generator capabilities for free/low costIn general:Audio generator:Frequency range: 1Hz - 50kHzPower: 1mVpp to 5Vpp in 50Ohm or 600Ohm (an audio standard impedance)Modulation: sometimes sine, square, gated, arbitrary (if a so called "arb waveform generator") log sweep etc.Distortion: usually low for high quality units.Function generator:Frequency range: 1Hz - 20MHzPower: 1mVpp to 5Vpp in 50OhmModulation: sine, square, gated, arbitrary (if a so called "arb waveform generator") log sweep etc.Distortion: medium -40dBc harmonicsRF Generator ("signal generator")Frequency range: 100kHz - >1GHzPower: -100dBm to + 13dBm (20mW)Modulation: AM, FM, modern ones have digital modulation forms as wellDistortion: high harmonic (-30dBc)

author: devanno
author_rank: Regular Contributor
timestamp: January 02, 2015, 05:52:26 pm
content: As all the great responses have indicated, you have multiple choices. Since you're into various projects, do you have time to build a DIY model? I just ran across this today:http://electronicdesign.com/analog/audio-function-generator-provides-three-simultaneous-square-triangle-sine-waveformsThere are a few links at the bottom of that page that may also be of interest vis-a-vis the sound card options for signal generation.I just did a quick search on Amazon.com also, and found audio generators for under $100 that may meet your needs, such as the B&K Precision 3001 (20Hz - 150kHz) for $85 ... it doesn't do sweep functions, just discrete outputs. I suggest if you consider this you read the reviews. In fact, I kind of like this unit myself so may add it to my kit. :-)Best wishes, and let us know what you decide upon, please!

author: devanno
author_rank: Regular Contributor
timestamp: January 02, 2015, 06:05:39 pm
content: Replying to myself (kind of like trying to get the right answer... heh) ... I looked up the BK Precision 3001 on Tequipment.net and found that they have it in stock for $73.95, less than the Amazon price (no big surprise there!).

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 03, 2015, 12:53:13 pm
content: Quote from: larry42 on January 02, 2015, 12:07:44 pmTrue! OP didn't tell us what his real purpose is. If it's just generating audible frequencies, no function generator, arb or even second hand old HP Wien bridge based stuff can beat the low distortion of a good sound card regarding cost. Good software I can recommend is ARTA:http://www.artalabs.hr/index.htmWith a 192 KHz sound card you can generate and analyse tones up to 90 kHz. Trial version is fully functional and doesn't time out, you only can't save waveforms and measurements. It was once free (university work) but due to complaints of commercial "colleagues" they decided to ask a small license fee.Also good software for a "soft" measurement set up with a sound card comes fromhttp://www.virtins.com/It is not free but also not expensive. Their licensing scheme however is really nasty (HDD locked) but the product is fine.Nowadays audio amplifiers tend to have higher bandwidth to over 1 MHz. GBP to 100 MHz is not uncommon. If you are up designing and/or troubleshooting such gear then you need something that can generate higher frequencies and an oscilloscope in that range to handle stability issues and so on.

author: KJDS
author_rank: Super Contributor
timestamp: January 03, 2015, 03:26:27 pm
content: I've just plugged in an old HP3310A function generator into a Keithley 2015THD.I set the HP3310A to 1kHz on the dial and measured 998Hz. Distortion is 0.07%

author: riverrat373
author_rank: Contributor
timestamp: January 03, 2015, 04:44:50 pm
content: Thanks for all the suggestions!

author: jpb
author_rank: Super Contributor
timestamp: January 04, 2015, 10:44:41 pm
content: Quote from: KJDS on January 03, 2015, 03:26:27 pmThis inspired me to do the same with my Agilent 33522A which I bought some months ago from the Agilent(now Keysight) ebay store but haven't had any chance to play with.Taking 10 harmonics for the THD and the 1kHz signal the distortion is less than 0.012% (the spec is < 0.04% up to 20kHz) - of course the 33522 is much newer (though not as new as the 33622) and costs a lot more (though, again, not as much as the 33622) but it shows that modern DDS generators compare well with older dedicated Audio sources at least as far as THD.

author: radhaz
author_rank: Regular Contributor
timestamp: January 05, 2015, 05:09:44 am
content: If super low distortion is a requirement:http://amp8.com/amp-etc/etc-etc/vp-7723a.htm

author: rf-loop
author_rank: Super Contributor
timestamp: January 05, 2015, 10:52:22 am
content: I do not know what is "Super low".But perhaps this is one what can call Super low THD oscillator.Down to class: 0.00001%http://www.janascard.cz/PDF/An%20ultra%20low%20distortion%20oscillator%20with%20THD%20below%20-140%20dB.pdf#######################################################################And just for some reference about economy class function generator: Siglent SDG1000 series DDS Arb/function generatorSpecifications: THD <20kHz = < 0.2%Harmonics level DC-1MHz -60dBcI have measured THD between 20Hz - 20kHz.It depends voltage level and some amount about frequency.Keithley 2015THD show values <0.03 - <0.1%Also this my one test result tell something about this.1kHzSDG1010 phase noise with HP8568B. (note grey area where HP Spectrum is limiting factor and it is possible phase noise in this area is better than image show or same but not worse - and still this HP is moderate good for phase noise measurement). (made with HP because in this time I did not know how this measurement system works with better R&S spectrum.It can say that this can well use also for "normal" audio things if do not go to special "audiophile" or "state of art" level.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 05, 2015, 05:17:40 pm
content: Quote from: rf-loop on January 05, 2015, 10:52:22 amState of the art at the moment is theApx555with a specified residual THD+N of -120 dB and up to 1 MHz.Attached a picture of my DG4102. Pretty good for a standard universal bench generator. It shows up some mains related spurs that look like coming from a ground loop. Probably from the Y caps of the mains filter. These are still there powered off in Stdby mode but disappear when I disconnect the generator from the mains.

author: Lightages
author_rank: Unknown
timestamp: January 05, 2015, 07:34:20 pm
content: I think you are confusing the OP with details he doesn't need. I think that for audio work a sound card can't be beat. Get something like this free:http://www.sillanumsoft.org/or any of the other many free scope/function generator programsOne hardware option, the Velleman HPG1:http://www.amazon.com/Velleman-HPG1-Pocket-Function-Generator/dp/B006YTWMZWThis gets you a good audio use generator with log sweep and up to 1MHz. $100 and it will do most of everything you will need.Most people don't need sweep functions at the beginning so for a tight budget this would be a good one. Really tight budget!http://www.ebay.com/itm/DDS-Function-Signal-Generator-Sine-Square-Sawtooth-Triangle-Wave-noise-Frequency-/191347257637?pt=LH_DefaultDomain_0&var=&hash=item2c8d2f7125A completely unknown but interesting option is this:http://www.ebay.com/itm/24Mhz-Dual-ch-DDS-Function-Arbitrary-Waveform-Signal-Generator-sweep-Software-/121496848485?pt=LH_DefaultDomain_0&hash=item1c49c6c865I briefly considered this one but decided to get something known, a Siglent SDG1025.There are some analog function generators available but their bandwidth and price do not usually match the value of modern DDS types.

author: _Wim_
author_rank: Super Contributor
timestamp: January 05, 2015, 07:53:32 pm
content: This is the result I get with my soundcards (EMU 1212M PCIe)

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 05, 2015, 08:31:08 pm
content: Quote from: Lightages on January 05, 2015, 07:34:20 pmAt least it gives a good overview of the possibilities. And yes a sound card is unbeatable at performance cost ratio, if it concerns audio frequencies. B.t.w. I didn't manage the sillanumsoft software to run stable on my PC, as do many other freeware solutions in this area.What can be squeezed out of a good soundcard is as near top dedicated expensive equipment, although over a limited range. Attached a pic of a M-Audio Audiophle192 PCI card. I replaced the standard NE5532's for more modern LM4562 ones. But this gave only a factor 3 of improvement over the already low distortion of the card. Not so much worth the effort.