Speakers are usually a nominal 4 or 8 ohm load.
Lo-Z microphones are a nominal 250 ohms.
A high-Z dynamic microphone or normal instrument pickup is usually a nominal 10k ohm impedance.
Under bridge piezo pickups usually have a native impedance around 1 Meg ohm for the pickup itself. If there are active electronics part of the reason is to match the impedance.
Generally you can drive a lower impedance source into a higher impedance input without problem but not the other way around.
If you have a true high impedance source plugged into a true low impedance input the mismatch can cause distortion.
The first two inputs of my XAir 18R specify that the 1/4 input (at least) can be used as direct input for instruments. Since they specify those two inputs it indicates that their normal input circuitry is actually designed with a lower impedance, probably 600 to 1K ohms. That mismatch could be the source of your problem.
Impedance problems were more often seen with tube circuitry. They are seldom a problem with solid state circuitry. Solid state tends to be high to very high impedance on the input side and low to very low on the output side. Still for best/cleanest transfer it is best practice to match the source output impedance to the nominal input impedance of the load. In this case the load for the guitar is the input of the UMC-404.
Last edited by Wink0r; 11-02-2018 at 09:10 AM.
I'm going to disagree with that last post a bit.
Most signal sources these days are happiest working into an actual load that is at least 10x their own rated impedance. If you look at the specs on most modern mic preamps, the ones specified for low impedance mics actually present a LOAD of more than 1k, sometimes more like 2K. This is not always made clear in the lit, but it is a fact of modern design. Solid state instrument amps can be made with a wide range of input Z, but higher impedance inputs are preferred for any passive instrument.
Instrument pickups might in some cases be a 10k source impedance, but the pots in a guitar or bass are often more like 250k, and the actual input impedance of most tube instrument amps is seldom less than about 470k, and can go much higher. If you are going to run a DI off the instrument and feed an amp at the same time, you want the DI to have an input impedance at least 10x that of the amplifier so that it does not load down the pickups and thus change the sound. The Countryman DI that I prefer to record with has a 10 Meg input impedance, which is about right for the way I use it.
Impedance problems with tube circuitry are almost always a matter of the speaker presenting the correct impedance to the amp output (tube output amps are indeed fussier about the load they see than are most solid state designs). The input of a tube amp is not likely to ever present an impedance mismatch problem to an instrument, because it provides a proper bridging load (meaning load impedance at least 10x the source impedance). Solid state amps may or may not be properly designed with a high enough input impedance for passive pickups, especially if you try to use an amp that was not specifically designed for passive guitars and basses. A keyboard amp may very well have too low an input impedance for a guitar, but a guitar amp will not present a load impedance problem to a keyboard instrument.
The one place where you want source and load impedances to MATCH is from a tube amp to a speaker. At the input side of an amp, you do NOT want to MATCH impedances. You want what we call a "bridging" rather than a "matching" load, meaning the impedance of the load (amplifier input) is at least 10x the impedance of the source (instrument output).
Good day,
Thus far, the configuration of my sets with SAC and SAW are going very well.
Interestingly, the Ampsim loads much quicker on the laptop than on the desktop. Also, with a buffer setting 1x128 at 44.1, I have had no slipped buffers!. Well done Bob and Behringer!
I am having a few minor issues with the Behringer and thus far, "I have received no love from them!"
My main concern is with regards to the sample rate always reverting back to 48000 KHz from 44100 KHz on a cold boot. This situation is particularly annoying in that there are "click's and pops" each time I launch SAC as it resets the ASIO drivers. I would very much prefer NOT to have to configure the SAC for 48000 KHz. As I said, I have yet to hear back fro Behringer support.
Any comments on 44.1 versus 48?
Let SAC be the master clock and set the Behringer to be the slave... then SAC will control the rate for each session.
Bob L
Bob,
...I see no way of doing this.
As far as I have been able to ascertain, there is nothing in the UMC Control Panel that allows for the UMC 404HD to be set as the Slave.
* I am using the most recent driver which is v3.48.
What is particularly disconcerting is that there no documentation available that explains how to use UMC Control Panel.
For SAC:
The Mixer > SampleRate option is set to: 44100
The Mixer > Resolution option is set to: 24 Bits
The following is the Status tab of the UMC Control Panel with the "Current Sample Rate" at 48000 Hz:
Attachment 2845
This is the Format tab:
Attachment 2846
This is the Buffer Settings tab:
Attachment 2847
Note: I have no idea what the "Safe Mode" option is for. There is no option to manually set the sampel rate either.
On enabling LIVE mode in SAC, I then observe the following:
Attachment 2848
Note: It is at this point where I hear "click's and pops" each time this ASIO drivers are reset.
After the ASIO drivers have been reset, I then observe the following:
Attachment 2851
I am somewhat at a loss here.
Last edited by mr_es335; 11-03-2018 at 08:37 PM.
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Philip G.
cgrafx,
...I have just "heard" that 48khz is not one to use...but that you should rather always double the frequency - so 88.2khz is supposedly preferable over 48khz???Is there a reason for wanting 44.1 instead of 48khz?
...I do not record and do not plan to record.If you are recording the audio for use with any video its going to end up being 48 anyway. You'll also get the added benefit of slightly lower latency, although not a huge difference from 44.1 to 48k.
I guess, when "push-comes-to-shove", I have always used 44.1khz so I always move in that direction. I will test out 48khz and see were that gets me.
There is nothing magical about 44.1 or 48 or 88 or 96 kHz it really just depends on what your intended purpose is and what you will or might be doing with the material in the future.
If the recordings are going to end up as traditional CD's than 44.1 kHz is an appropriate sample rate as that is what the end product will be
If the recordings are going to end up used in a video than 48 kHz is generally going to be the appropriate sample rate.
the 88.2 and 96 kHz double rates are for the most part really specialty rates and would not be used unless you explicitly have a need to do so. They take up twice the storage space, require double the processing resources and in most current day circumstances don't provide any real sonic advantage over 44.1 or 48 kHz.
If this is really just for your listening pleasure than 44.1 or 48 will work just fine and since your having problems getting the system to remember 44.1, just leave everything at 48 kHz and be done with it.
Last edited by cgrafx; 11-04-2018 at 10:46 AM.
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Philip G.
cgrafx,
...Philip, as always, your advice is always to the point and very helpful. Much appreciated....and since your having problems getting the system to remember 44.1, just leave everything at 48 and be done with it.
I assume however, that I will have to redo any/all wave files to the newer format? Correct? can this be accomplished within SAW - or do I perform this operation externally?
PS: I just "discovered" that I will need to re-do all of my sessions to the newer format. This will indeed be a bit of a chore. I guess I will just have to wait and see what assistance Behringer provides.
Last edited by mr_es335; 11-04-2018 at 10:26 AM. Reason: Discoveries
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