I/O ping returns the same value on every buffer size

bencuri wrote:

00:00:00:00.04

Now what does this mean in samples? I have no clue about these measurements Unfortunately.

That is a SMPTE time format displaying the additional subframes

hh:mm:ss:ff:subframes

To calculate subframes into samples, you have to use the current Sample Rate and the Frame Rate in your project.

For example:

Sample Rate

44100Hz = 441000 samples/sec

1 sample ➤ (1/44100) ➤ 0.02ms

Frame Rate

25fps (frames/sec)

1 frame ➤ (1/25) ➤ 40ms

1 frame ➤ 80 subframes

1 subframe = (40ms/80) = 40ms/80=0.5ms

4 subframes = 2ms

2ms/0.02ms= 100 samples

That means, the 4 subframes you measured are 100 Samples long at a Sample Rate of 44.1kHz and a Frame Rate of 25fps

If you don't want to torture your brain with math, you can let Logic do it for you.

The Preference ➤ General ➤ Displays lets you choose the Time Scale that is used in the Control Bar Display and the Rulers. I guess this is the setting you have in your project showing the SMPTE with subframes. You will the 4 Subframes.

If you switch the setting to display Samples, then the LCD will show the same time in that Time Scale, 100Samples

Hope that helps

Edgar Rothermich - LogicProGEM.com

(Author of the "Graphically Enhanced Manuals")

http://DingDingMusic.com/Manuals/

'I may receive some form of compensation, financial or otherwise, from my recommendation or link.'

Whatever click you use, it should have a sharp attack, I think a Clave would fine, or a rimshot.

You need to dismiss the idea from your mind that the I/O Buffer (128, 256 512 1025...etc) is important or has something to do with this measurement. Forget it! The only reason it could make any difference is if the Alesis Core Audio driver reports an incorrect number of samples to Logic's audio engine. The I/O Buffer is automatically compensated for by Logic... it does not come into play with the measurement your taking. As I said, 90% of the time the Recording Delay slider should be left at zero samples, (center position)

The Recording Delay offset is only to fix audio drivers that are not reporting the correct position to Logic's audio engine.

You need to drop your preconceptions of how Logic compensates for latency, you have a couple of things wrong that are messing you up. I appreciate your willingness to experiment.

All this is in the manual. http://help.apple.com/logicpro/mac/10/#lgcpbb81aca5

Next is to investigate Low Latency Mode. It has a very specific function. I see people post that leave it on all the time and say they can hear a difference when it fact it's no effect at all. Low Latency Mode, with help your recording line up correctly when using plugins that require look-ahead technology. Like "Multipressor." There are a certain class of plugins that Logic can't compensate for.

P.S. the Second image looks perfect, don't know why the horizontal image is showing an error, the vertical sample looks right.

That IS NOT what the I/O plugin is designed for. The I/O plugin is for hooking up external gear like a compressor or reverb unit or foot pedal. It's not going to change values because of the I/O buffer size. It's designed to measure the latency inherent in an external effects device and send the offset to Logic, just like a delay inducing plugin that Logic compensates for.

The correct method for adjusting recording delay is to use a loopback test while recording audio. Most of the time recording delay can simply be left at zero, it's up to the audio drivers to report the correct latency to Logic's audio engine so Logic can compute the offset required. Leave the I/O Buffer out of the equation.

The recommended manner for a loopback test is to connect a short (analog) cable from an output 1 to input 1 of your audio device. Make sure Software monitoring is off. Created an MIDI/Instrument track with 8 bars of quantized quarter notes, use Klopfgeist as the output Instrument, turn Metronome off to avoid doubling the click. Record a track of the 1/4 note click, zoom in and check the start of the recorded audio click, this is where your offset will be,( if there is one). If there is an offset use recording delay to place the recorded click at the very start of each beat. You will have to repeat the record process several times to do this.

Next, delete the MIDI 1/4 note track and enable the metronome, try the test again using Logic/Klopfgeist as the click generator, It's bad troubleshooting technique to assume anything.

Recording Delay only affects the placement of the recorded audio.

Now you can look at buffer size as each buffer size may or may not need separate recording delay settings, also different sample rates may require separate recording delay settings.

bencuri wrote:

Okay, so I did it. However it was not easy. For some reason the click recorded was not visibe in the signal view, I had to adjust gain with +30db so it would become visible, even if I set every volume near to starting feedback.

If you're having any type of feedback you did not follow my instructions exactly.

bencuri wrote:

Exactly the amount that the I/O plugin ping returned. I guess this will be the correct one, probably the clave sample had some silent part in the beginning and that's why it was not visible and confused me. But with the klopfgeist, it is 30 all the time.

Anyway, it was in a video on Youtube where it was mentioned that the lanetcy offset will change by buffer size. In case I use my iMic as interface, it is like that, but in case of the Alesis iO4 it is standard 30. So in this case Logic seems to compensate. It was just not the case with Reaper, that's why I was confused.

I also wanted to ask the plugin latency "Low latency mode" option. It is set to off for me, because I was unsure what to set as limit. How can I investigate it?

Some drivers do change the latency offset slightly with different buffer sizes, I had an RME audio card setup that didn't change for any of the settings.

Ok, here's the reason why you need to do it the recording way. You do need to alter the recording delay slightly if you want it perfect. However, you can't do it with the I/O buffer, you can only do by the recording comparison. Because you have to see where the waveform starts in comparison to the MIDI click. So, start experimenting with the "Recording Delay" slider, which will end up opposite the direction you think it should go.

Save Low Latency Mode for later, it should normally be off.

Leaving the buffer at 1024 is ok but may be overkill, it might make Logic a bit less responsive, I would leave it at 256 and go up from that only if there were problems with playback and/or overload messages.

For the test, make sure Preferences-Audio Software monitoring is not checked. Also in Logic's Preferences-Audio, make sure the Alesis is set as Both the Input and Output device.