how to determine phase past 360 degrees - Page 1
Forum section: electronics / projects

author: brownt
author_rank: Regular Contributor
timestamp: June 25, 2018, 10:55:22 pm
content: I want to measure the delay in an audio system between input and output. Due to the signal processing I think it is around 50mS as I can hear the delay. How can I measure that delay time? I tried phase on an oscilloscope, and it is different, but if its over 360 degrees then it doesn't tell the delay time

author: ahbushnell
author_rank: Frequent Contributor
timestamp: June 25, 2018, 11:04:05 pm
content: Quote from: brownt on June 25, 2018, 10:55:22 pmPut in a single pulseSent from my SM-G930V using Tapatalk

author: brownt
author_rank: Regular Contributor
timestamp: June 26, 2018, 01:53:03 am
content: thanks. how do i create a single pulse. It is not an option on my signal generator.

author: CopperCone
author_rank: Super Contributor
timestamp: June 26, 2018, 01:54:28 am
content: i think that would be considered a marker signal if you are looking to buy the capability.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: June 26, 2018, 02:13:42 am
content: Quote from: brownt on June 26, 2018, 01:53:03 amSet it to a narrow pulse. It may be called duty.Sent from my SM-G930V using Tapatalk

author: DaJMasta
author_rank: Super Contributor
timestamp: June 26, 2018, 02:42:10 am
content: You may also be able to use an external trigger to turn on the output (or just to make a pulse), and then just probe the trigger signal on the scope and single shot capture.In the same way, you may be able to probe the sig gen output and then the audio system output, single shot capture triggering on either and if you've got the memory depth, you'll catch the start point on both.

author: rstofer
author_rank: Super Contributor
timestamp: June 26, 2018, 03:06:00 am
content: Quote from: CopperCone on June 26, 2018, 01:54:28 amA very slow square wave. If you want, you can get a positive and negative pulse by using a differentiator circuit (resistor/capacitor) on the input.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 26, 2018, 03:10:36 am
content: In principle, you can just use a lower frequency such that there is no ambiguity. The problem you might have is that your audio system might not go low enough in frequency. You can also use a narrow pulse at low rep rate, or possibly a tone burst to get around the low frequency limit of your system.However, there is a simple way to get this from the data you are already collecting. Delay is a phase that is linear in frequency. So you just need to measure phase vs. frequency, then plot it and find the slope.50 ms is 360 degrees / 20 Hz or 18 degrees/Hz. So measure the phase shift at 100 Hz, 101 Hz, 102 Hz, and so on, maybe up to 120 Hz. You should see a line (excepting any phase wraps). Find the slope of the line in degrees/Hz and divide by 360 to get the delay in seconds.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 26, 2018, 02:19:33 pm
content: Download "Holm Impulse" software...Use a sound card...Steve

author: CJay
author_rank: Super Contributor
timestamp: June 26, 2018, 03:18:14 pm
content: Signal generator* with external trigger capability, trigger it with the output of the audio device, put the scope on the input or the output and the nunber of divisions between pulses is your delay time.*you may even be able to use something as simple as a 555 timer

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 26, 2018, 03:49:27 pm
content: Well, past 359.999... degrees, I wouldn't call it a phase difference, but more like a delay. Phase only makes sense over one period IMO.Anyway, as everyone has told you, you need a causal reference. May also be interesting to distinguish group and phase delay:https://en.wikipedia.org/wiki/Group_delay_and_phase_delayYou just need to generate an input signal with a definite start, and measure the delay between the start of the input signal and the start of the output signal. It can be a single pulse or a sine (allowing you to measure the delay for specific frequencies). You can do this with a triggerable signal generator or a computer with a decent audio output.

author: Bassman59
author_rank: Super Contributor
timestamp: June 28, 2018, 02:29:26 am
content: Quote from: brownt on June 26, 2018, 01:53:03 amA long time ago I created aWAV file of a delta function. The sample rate is 48 kHz. It's one sample at 0 dBFS and all other samples at zero.Or you could use a program likeSmaartto generate the stimulus and determine the impulse response, and hence the delay, for you.Also, it is super instructive and interesting to look at the audio DAC’s output when the source is this delta impulse. That’s an exercise left to the reader!