Smart phone as signal generator vs dedicated device for audio testing - Page 1
Forum section: electronics / beginners

author: gfmucci
author_rank: Regular Contributor
timestamp: June 06, 2020, 08:48:30 pm
content: For audio testing, is there any significant benefit to using a dedicated signal generator versus a smart phone app, like the one linked below that produces a 1 to 22KHz square, sine, sawtooth or triangle wave through audio amp being tested by an oscilloscope. Any cautions for using the phone for this purpose?https://play.google.com/store/apps/details?id=com.luxdelux.frequencygenerator

author: rstofer
author_rank: Super Contributor
timestamp: June 07, 2020, 12:48:22 am
content: Mostly, the app description talks about sound through the cell phone speakers. It only briefly mentions testing headphones, presumably with the headphone jack, it the phone has one.The speaker related stuff is not helpful. Further, if I were going to make a jumper cord from the headphone outlet, I would want to put a large capacitor (like 100 ufd) in series with the signal to prevent any kind of DC coupling between the device being tested and the cell phone.I don't think I would do this. It's too easy to do something similar with a PC sound card and it is generally safer for the equipment. There are some inexpensive signal generators around as well. The question comes up about THD - how clean is the source? Sound cards do pretty well, low cost signal generators may be pretty awful. Real Arbitrary Waveform Generators can be very good. It depends on what you expect.If it was for injecting a signal into a device that isn't working, I would buy one of the cheap signal generators and save on my cell phone or PC.

author: gfmucci
author_rank: Regular Contributor
timestamp: June 07, 2020, 01:11:30 am
content: I don't understand the problem with driving the amp (the device to be tested) with the signal generated by that sort of app through the phone plugged into the amp input just as any music player would be. A signal is a signal, whether a square wave or music. As far as signal quality, the sound generated by the Samsung S9 phone sounds quite clean through a variety of headphones and ear pods, but yes, I have not specifically tested how clean the phone output is. I have plugged headphone outs from a variety of phones and tablets into the inputs of integrated amps without issue. So it appears the issue may be to distinguish distortion generated by the phone from that which may be created by the phone.

author: ArthurDent
author_rank: Super Contributor
timestamp: June 07, 2020, 01:29:51 am
content: Try the 'Keuwlsoft Dual Channel Function Generator' on your android phone.https://play.google.com/store/apps/details?id=com.keuwl.functiongenerator&hl=en_US

author: gfmucci
author_rank: Regular Contributor
timestamp: June 07, 2020, 03:09:49 am
content: Quote from: ArthurDent on June 07, 2020, 01:29:51 amYes I already had both installed on my phone. Just different interfaces. They both appear to do the same.What are the amp outputs that go into the scope, speaker out or high impedance out? I guess it just depends on whether testing preamp or power amp. Use 10x probe in either case?

author: rstofer
author_rank: Super Contributor
timestamp: June 07, 2020, 07:44:46 am
content: Quote from: gfmucci on June 07, 2020, 01:11:30 amIt's likely no problem if the amp is known good. OTOH, if the amp is being repaired or, worse, breadboarded, I'm not sure I want to risk my only cell phone. It would be far cheaper to buy one of the $50 audio signal generators. I don't have one of the really expensive cell phones but I would sure hate to have to replace it.But, it's a choice. If the amp is known good then maybe it's fine. I'm not going to do it but other people will have different opinions.