Can you hear the hissing in both your headphones and speakers?

I would imagine this is frequency related and not key range related. In other words, if you pressed the octave down key 3 times then you would hear no artifacts. Also, I imagine some performances may be better than others. And pressing the octave up key 3 times would infect even more of the octaves with the artifact.

If all of this is true including no artifacts using headphones, then some issue with your monitors is likely. Or if running through some amp, preamp, mixer, etc - then something with it.

It's not entirely clear if you are listening to main outputs, assignable, earphones, or USB (digital) through your computer.

It would be helpful to list your setup components and how they are connected (cable type and what each end is plugged into).

I tested with lowering octaves down and the hissing noise did not happen with the same keys at high end of the keyboard. So it is frequency related and the hissing noise comes along at high pitches. The noise is more pronounced if you use string sounds with long sustain (like violin, viola, etc.) and you press and hold the key down hard to get a louder sound.

Following are my connection setups. I tested with these setups one by one and the hissing noise happens with all of them.
(1) Montage-8 is connected to Behringer Ultratone KXD15 combo-amplifier using two balanced 1/4" TRS cables (Stereo).
(2) Montage-8 is connected to Focusrite Scarlett 18i8 audio interface using two balanced 1/4" TRS cables (Stereo). The Scarlett 18i8 output is connected to two JBL studio monitors.
(3) Montage-8 is connected to AKG M80 stereo headphones.

Did you update the OS to V1.5?

I have just updated my Montage-8 firmware from 1.02.0 to 1.50.0.
The hissing noise issue is still there.
It is a constant low-frequency hissing noise (about 40-50 Hz) that follows the instrument sound at high pitches.
Any idea on how this might be attributed to, firmware, hardware design flaw or hardware defect?

I have just updated my Montage-8 firmware from 1.02.0 to 1.50.0.
The hissing noise issue is still there.
It is a constant low-frequency hissing noise (about 40-50 Hz) that follows the instrument sound at high pitches.

Sorry you are hearing an unwanted sound from your Montage, let's eliminate keyboard amp, and the audio interface completely from the system, just use the headphones. Completely disconnect the amp and interface. Listen to the headphone...and please give a better description of what you are hearing.

"Hiss" is a word usually attributed to high pitches, while 40-50Hz would clearly be described as "rumble" at least to most mortals - so, which is it? High pitched or extremely low pitched.

The lowest note on a bass is approx 41Hz - and clearly would be described as a rumble. "Low-frequency hissing" is a paradox.

Any idea on how this might be attributed to, firmware, hardware design flaw or hardware defect?

Can't make that determination quite yet.

Hi Brian,

don't worry, I think I know what you hear. This is normal. I can create it on my Montage 6, when transposing up. This is an inherent artifact of sampling based synthesizers. It happens when the playback frequency is too far above the frequency in which the sample was recorded. I get that with my Montage, with a Nord Piano 2, a Roland Integra and all other digital sampling based synthesizers I owned over the years. It is not the same but somewhat related to was is termed aliasing (see http://www.earlevel.com/main/1996/10/20/what-is-aliasing/ for a good explanation). Analog synthesizers don't suffer from that and digital modelling based synthesizers don't necessarily have it as well.

For a final confirmation, you can test this with for example the "Chamber Strings" preset which exhibits this pretty strongly. In contrast if you go to "Category Search", "Init Normal (FM-X)" you get some sine sound which is not sample based (well...). You should not hear sucht artifacts. Well at very high frequencies you hear some other frequencies which do not really belong there. But they are just sines at different frequencies.

BM: his testing already included testing with headphones only. At least, I'm assuming the "(1), (2), and (3)" configurations are isolated and his headphone only (AKG) test did not have speakers running in the background.

... I tested with these setups one by one ...
(3) Montage-8 is connected to AKG M80 stereo headphones.

The clarification on what hissing means is valid. You have a digital recorder, why not record the sound and save in a format which clearly demonstrates the issue you are hearing and upload here as a ZIP file (maybe call the file Montage_PERFORMANCENAME_hiss.ZIP - where PERFORMANCENAME is the preset performance you used)? That would probably be preferred as uploading to a site like http://clyp.it may change the sampling rate or # of bits and change the sound enough that the artifact is no longer clear.

At least it would document what you are hearing and others can compare with what they hear playing the same performance and notes.

My frequency estimate of the noise might be wrong and way off.
It might be the aliasing effect that Stefan explained. Thanks, Stefan.
When I tested with the headphones, the keyboard amplifier was disconnected and nothing else was connected except the headphones.
I made a brief recording using the Seattle Sections performance using Montage's internal audio recording to USB memory stick.
The recorded file is attached.

My frequency estimate of the noise might be wrong and way off.
It might be the aliasing effect that Stefan explained. Thanks, Stefan.
When I tested with the headphones, the keyboard amplifier was disconnected and nothing else was connected except the headphones.
I made a brief recording using the Seattle Sections performance using Montage's internal audio recording to USB memory stick.
The recorded file is attached.

My frequency estimate of the noise might be wrong and way off.
It might be the aliasing effect that Stefan explained. Thanks, Stefan.
When I tested with the headphones, the keyboard amplifier was disconnected and nothing else was connected except the headphones.
I made a brief recording using the Seattle Sections performance using Montage's internal audio recording to USB memory stick.
The recorded file is attached.

Yes, that's the same mine sounds! So there is nothing wrong with your Montage.

... or maybe "there's nothing different with your Montage". "Wrong", in this case, would be a subjective call by the musician of what comes out of Montage vs. expectations. ... and this is being presented as something the OP doesn't want from his strings - so maybe there's a way to clean up the given performance with some settings (performance parameter changes including effects).

In cubase, I was able to reduce the noise using High Pass I filter type w/0.0dB gain and the EQ frequency at 2.828kHz. A fairly aggressive EQ targeted at just the notes you played. There's a way to apply filters progressively as you move up the scale - so it could be possible to target only high notes with such a filter.

I do not have the keyboard plugged in - so the information is in terms of cubase instead of Montage at the moment. You should be able to find an HPF (high pass filter) that can filter out most of what's below around 900Hz and achieve similar results (noise floor improvement).

Then I was way off. I thought perhaps a small snake was stuck under the keybed in that range and whenever you smashed down on him he would hiss back. 🙂 What ya'll are describing is completely intuitive. I've always known about not being able to "stretch" samples beyond their limits but I never made that connection that this was the issue in this post. Seems plausible that you'd get an unrealistic sound because at some point they simply stop sampling instrument notes above a certain reasonable range and beyond that you're hearing stretched samples. I play the trumpet and nothing sounds better than a trumpet screaming at 3 octaves up. But then try to reproduce that note on Montage when they didn't sample that trumpet note 3 octaves up (only 2 maybe) and it sounds horrible when stretched up an extra octave.