Front vs. Rear Input Question

[mworkman]

I know you don't want to hear it but if you spent as much time and energy plugging your guitar in and working on presets that sound good as you do trying to figure out if your unit is "broken" or not you'd have all your patches ready.

When you plug your guitar in and play through the presets does it sound good to you? Can you make some "tweaks" that would make it sound good to you? Spend your time on that.

Or at the very least... send the unit back and have support check it out. If Fractal says it meets specs then have them send it back to you and get to work playing music. If it doesn't check out you can either (a) have them keep it and get your money back (if its within the trial period) or (2) have them fix it and send it back.

 

[Jay Mitchell]

it was , 1st , sound direct,

Not so fast. What kind of playback device? That makes a difference.

then sound via analog rear

Which sounds very similar. What exactly do you mean by "direct?" What device sees the output of your playback unit?

the again direct i think , i do'nt remember and the last (muddy) was analog front ...

Which you obviously were overdriving. That's what makes the HF rolloff that is so obvious.

 

[sampleaccurate]

You did something wrong. The front input is flat.

With all due respect sir, I have endeavored to replicate your results using the front input without success. I have spent over 8 hours checking, testing, checking, re-testing, all with exactly the same results.

I'm not claiming that I'm not doing something wrong. I am respectfully asking, before committing more of my time to this issue or sending my unit in for testing, if the firmware is responsible for high frequency de-emphasis and if so could there be a defect in the latest version that was not caught in testing? Or in other words, was your test that yielded a flat response performed with pre 8.09 firmware or was 8.09 used?

The chorus didn't work properly the day I got the unit (8.08), so it doesn't seem outside the realm of possibilities that a second error exists in the firmware. I'm just respectfully asking if you've checked this out because it's not something that's immediately obvious on most patches, especially those with heavy distortion. But on bright clean tones there's a noticeable (clearly audible) difference between the front and rear inputs with the input parameter set properly.

Thanks for your time.

Stephen Cole

 

[sampleaccurate]

I know you don't want to hear it but if you spent as much time and energy plugging your guitar in and working on presets that sound good as you do trying to figure out if your unit is "broken" or not you'd have all your patches ready.

When you plug your guitar in and play through the presets does it sound good to you? Can you make some "tweaks" that would make it sound good to you? Spend your time on that.

Or at the very least... send the unit back and have support check it out. If Fractal says it meets specs then have them send it back to you and get to work playing music. If it doesn't check out you can either (a) have them keep it and get your money back (if its within the trial period) or (2) have them fix it and send it back.

It's going to take literally months to reprogram HUNDREDS of tones. It took years to develop the existing ones.
Some songs have 4 or 5 different sounds. We will use the majority of the over 380 program locations in the AXE.

You have no idea how much work I'm about to commit to - not a clue. Take what's in your mind and multiply it by 100. I would have finished maybe 4 or 5 patches out of several hundred in the time I've spent testing. Then later when I load them into my second future AXE, assuming this one isn't working properly, all my tones are going to be wrong. I'm not spending months working on hundreds of tones for cover songs on a unit with an abnormal frequency response, whether it's due to my error or a defective unit or defective firmware. I need to find out and sending it back is a last resort.

This was built with the highest grade components so there's no reason to suspect a hardware defect yet.

If you want to see the extent to which we take our processing, here are some links to LIVE clips. The guitarist uses the Mesa Boogie Triaxis and Eventide Orville processor you see in the rack in the above post for the meat of the tones, with a Hughes & Kettner Blues Master power amp to complete the Triaxis preamp tone. All tones are pre-programmed and called up with a sequencer using MIDI program and CC commands.

http://www.rockonband.com/Comfortably_Numb.mp3
http://www.rockonband.com/Eruption.mp3
http://www.rockonband.com/Separate_Ways.mp3
http://www.rockonband.com/Tom_Sawyer.mp3
http://www.rockonband.com/Feels_Like_The_First_Time.mp3
http://www.rockonband.com/Crazy_Train.mp3
http://www.rockonband.com/All_Along_The_Watchtower.mp3

BTW, all the drums are a custom acoustic set I converted to an electronic kit with my own triggers and custom samples using GigaStudio3.

 

[mworkman]

Wouldn't sending it to Fractal be the quickest way then to confirm that your unit is working properly or broken?

 

[rdomain]

+1

 

[sampleaccurate]

Wouldn't sending it to Fractal be the quickest way then to confirm that your unit is working properly or broken?

If I'm doing something wrong (which is what Fractal told me was the case) then no, it would be an unnecessary delay.

 

[godprobe]

[quote="stef herbuel":1udokpjx]it was , 1st , sound direct,

Not so fast. What kind of playback device? That makes a difference.[/quote:1udokpjx]
I'm not a tech/audio guru, so my questions are just out of curiosity and don't have much basis in actual audio troubleshooting sleuthage...
- I might have missed it in the thread (apologies if I have), but I'd also be interested to know what the full signal chain is, including the software used to record the image and cables used.
- The "line level device" (regardless of level) mentioned in the first post has me particularly interested...
- Again, I'm not a guru, but why is the graph's main representation on the first image centered near 0 dB while the other one is centered near 5 dB?

Lastly, I'm hearing you on wanting to make sure that it's you and not the Axe-Fx that's making a mistake. I'm not sure why other forumers are telling you to just ignore the "problem" -- that seems kinda misguided to me. Wherever the inconsistency lies (and I sincerely doubt that it's within the Axe-Fx, *especially* not within the firmware), I hope you can find it.

 

[sampleaccurate]

[quote="stef herbuel":3sa9yqsj]it was , 1st , sound direct,

Not so fast. What kind of playback device? That makes a difference.

I'm not a tech/audio guru, so my questions are just out of curiosity and don't have much basis in actual audio troubleshooting sleuthage...
- I might have missed it in the thread (apologies if I have), but I'd also be interested to know what the full signal chain is, including the software used to record the image and cables used.
- The "line level device" (regardless of level) mentioned in the first post has me particularly interested...
- Again, I'm not a guru, but why is the graph's main representation on the first image centered near 0 dB while the other one is centered near 5 dB?

Lastly, I'm hearing you on wanting to make sure that it's you and not the Axe-Fx that's making a mistake. I'm not sure why other forumers are telling you to just ignore the "problem" -- that seems kinda misguided to me. Wherever the inconsistency lies (and I sincerely doubt that it's within the Axe-Fx, *especially* not within the firmware), I hope you can find it.[/quote:3sa9yqsj]

Good questions.

Sweep is constant amplitude from 20 -20 kHZ over 24 seconds (I've used different lengths) created by Voxengo Deconvolver.

Software is Sonar 8.31 for record/playback. Response measured with Vogengo Deconvolver and more importantly, my ears.

Audio interface (line level device) is a MOTU 2408 MKIII

The second graph is at -5 dB because I didn't normalize the IR file.

Lastly, all the tests on my rear input are near perfect which leads me to believe that I'm doing this correctly, but I'm still not going to make that claim.

I'm about to the point where if someone told me what parameter I have set wrong or what I'm doing wrong and "showed me the light" on how to get this to work properly that I'd start a new thread titled: "Stephen Cole is an incompetent idiot who can't take simple frequency response measurements".

Thanks.

Stephen Cole

 

[FractalAudio]

The inputs are swept as part of the functional test process so it would be unusual for there to be a problem. However, after reading everything you've done it sounds as though there may be a hardware issue, especially if you can hear a difference.

My advice is to use something other than Voxengo just to be sure. You can download a free version of TrueRTA here: http://www.trueaudio.com/rta_abt1.htm

It's great software and if you're doing audio work I highly recommend buying the pro version.

 

[sampleaccurate]

The inputs are swept as part of the functional test process so it would be unusual for there to be a problem. However, after reading everything you've done it sounds as though there may be a hardware issue, especially if you can hear a difference.

My advice is to use something other than Voxengo just to be sure. You can download a free version of TrueRTA here: http://www.trueaudio.com/rta_abt1.htm

It's great software and if you're doing audio work I highly recommend buying the pro version.

Thanks very much for the tip. I'm all over it.

Stephen Cole

 

[Shaloha]

I repeat my advice to you at the beginning of this thread. Send it in to Fractal to make sure its up to spec. I have worked in a number of scientific and research laboratories. All equipment is calibrated BEFORE running experiments. No sense running tests, if the equipment is not first calibrated and up to spec. Again, you are spending incredible amounts of time to find out if you are doing something wrong. All that is wasted effort if the unit is not up to spec. Send it in. If there is nothing wrong, then continue with your search...but it makes no sense to waste your time without first knowing if the unit has a problem. It's a very small delay compared to the amount of time you are spending on troubleshooting operator error, of which there may be none! Not intending to be antagonistic...just giving my best advice..

 

[sampleaccurate]

i did this test before (the file indicate january 14 / 2009) 1 month after buy the axefx ;-)
http://rbul1.free.fr/analogrear.mp3

it was , 1st , sound direct, then sound via analog rear (YES, I/O set to rear, volume matched, all shunt) ,the again direct i think , i do'nt remember and the last (muddy) was analog front ...

meh if all that is "transparent" cliff, my unit is defective, it's not possible , because you can hear it doesn't sound the same at all :shock:


excuse the "playback" for this test it's my JV1010 roland expander demo :lol:

I'm not getting nearly that much HF attenuation with mine. I think we have different problems. Your's is much worse.

 

[sampleaccurate]

The inputs are swept as part of the functional test process so it would be unusual for there to be a problem. However, after reading everything you've done it sounds as though there may be a hardware issue, especially if you can hear a difference.

My advice is to use something other than Voxengo just to be sure. You can download a free version of TrueRTA here: http://www.trueaudio.com/rta_abt1.htm

It's great software and if you're doing audio work I highly recommend buying the pro version.

Unfortunately the free version only performs 1 octave resolution spectral analysis (and only with white noise) so it's not going to do me much good unless I purchase the full version, and I might, it looks like a nice package.

But when I'm running a constant amplitude frequency sweep into the AXE and I watch the meter on the computer that monitors the input signal to the AXE stay rock solid in one place for the entire sweep and the output meter monitoring the return of the AXE output start to drop as it hits the cutoff point around 1.5 kHZ, I don't really have to use any analytical software to confirm the problem even though I have. I also used my ears.

Add to that the rear input is perfectly flat both when measured and to my ears, and a direct hard wire bypassing the AXE is even flatter (when measured).

Thanks for your time.

Stephen Cole

 

[stef herbuel]

I'm not getting nearly that much HF attenuation with mine. I think we have different problems. Your's is much worse.

this, (and this pb of harmonic i miss) drive me crazy :roll:
i really would appreciate if 2 or 3 persons post a clip like this from a cd or wathever,
direct, rear input , and front input , tell me where the knob are exactly etc
so i would use the direct file and try the same with my axe fx.

thanks if someone want to try this.

 

[sampleaccurate]

I'm not getting nearly that much HF attenuation with mine. I think we have different problems. Your's is much worse.

this, (and this pb of harmonic i miss) drive me crazy :roll:
i really would appreciate if 2 or 3 persons post a clip like this from a cd or wathever,
direct, rear input , and front input , tell me where the knob are exactly etc
so i would use the direct file and try the same with my axe fx.

thanks if someone want to try this.

I'm going to send my unit back for testing if I can't figure it out by Monday. If there is a hardware defect that's causing this it might be the same thing only worse in yours.

I can tell you that for my unit that unless you're playing a clean patch it's very difficult to hear the difference between front and rear. And even then I'm only getting 5 or 6 dB of attenuation at the top of the range of most guitar sounds which can be easily compensated for with EQ.

Assuming my unit is defective, 95 out of 100 people wouldn't notice it, and even then they wouldn't consider it severe. Your problem (based on listening to your mp3) is severe. I wish I knew how to help you. I ran the same program material tests and I didn't post them because although I can clearly hear the difference, I'm afraid other people won't we able to. As I said, it's not nearly as dull sounding as yours, but it's noticeable and measurable to me.

Good luck. I'll let you know how mine turns out if I send it back.

Stephen Cole

 

[sampleaccurate]

I've figured this out. I don't think it's a case of operator error or a defective product.

While I haven't managed to get the response of the front input as flat as the curves that have been posted, I finally managed to get it very close while manipulating the controls of the AXE with a RTA showing me the effects. I then verified my results by carefully taking measurements.

It appears that the level of the input signal going into the unit must be extremely low in order to avoid the high frequency limiting that Jay Mitchell first mentioned. Here's the thing - the level of the signal coming out of my guitar is strong enough to push the input into high frequency limiting. So while the reason my measurements were not showing a flat response was that the input level was too high, the input level first used in the tests was lower than that coming out of my instrument.

In addition, the limiting appears to occur prior to the input gain potentiometer so it cannot be eliminated by turning down the input pot. It appears to be solely dependent on the level of the input coming into the front jack. The signal appears to go through a the high frequency pre-emphasis and limiter prior to going through the gain stage that the potentiometer controls. At least that's what my tests are showing my unit is doing. I see no way to control the threshold of this effect, it seems to be preset.

There is probably a very good reason for this behavior that I don't understand, and I'm not going to ask. The manual clearly states that the front input is especially conditioned for electric guitars, I assume passive ones since the front input impedance is so high. I guess this is the special conditioning at work. One effect it has is to brighten your tone when you turn the volume pot on your guitar down, or prevent it from becoming as dull perhaps I should say. That's usually considered desirable.

In any event, it does not appear that the unit is defective, and the effect is subtle, at least on the vast majority of patches, when a normal input signal is used even though some limiting of the incoming high frequencies may be occurring. It looks worse on the curve than it sounds even when the input level is relatively high.

I'm satisfied there's nothing wrong and I'm getting back to work on tones and making some music. I do believe however that people with good ears, hot pickups or active preamps, and who use bright clean tones could notice a difference in the sound of the front and rear inputs. I believe those who say they can hear a difference because I can hear it and I can measure it at signal levels well within the normal output levels of electric guitars.

I could be wrong about some of the above, but those are my conclusions based on extensive tests and I'm reasonably confident about my findings. If I had better tools it would help. If I am wrong please let me know.

Thanks to Cliff at Fractal Audio for the link to the software that helped me solve my problem, and everyone else for their suggestions.

Stephen Cole

 

[Jay Mitchell]

It appears that the level of the input signal going into the unit must be extremely low in order to avoid the high frequency limiting that Jay Mitchell first mentioned.

Yes, if by "extremely" low you mean less than nominal line level (0dBu) but greater than nominal mic level (roughly -50 dBu).

There are reasons that this will not affect the sound of a guitar, though. Read on.

Here's the thing - the level of the signal coming out of my guitar is strong enough to push the input into high frequency limiting.

No. The level vs. frequency content of the guitar's signal has been taken into account in the codec process.

So while the reason my measurements were not showing a flat response was that the input level was too high, the input level first used in the tests was lower than that coming out of my instrument.

No. Setting the level below 2kHz of a sweep lower than the level of the guitar signal is not enough. The frequencies that will cause self-limiting are all at or above 2kHz, and the amplitude of a guitar's signal has much lower content above 2kHz than below. The levels of frequencies above 2kHz in a sweep are identical to the levels at lower frequencies.

In addition, the limiting appears to occur prior to the input gain potentiometer

Yes.

There is probably a very good reason for this behavior that I don't understand, and I'm not going to ask.

It is called "maximizing signal to noise." The response of the front input to a signal that contains the frequencies and levels that passive quitar pickups produce will be flat. Because of the frequency-dependent gain of this input, care is needed when using a broadband signal to analyze its performance, as you have discovered.

The manual clearly states that the front input is especially conditioned for electric guitars, I assume passive ones since the front input impedance is so high.

The input impedance of the rear input is the same (1 megohm) as the front.

I guess this is the special conditioning at work.

No. Input impedance and filtering/limiting are independent of each other.

One effect it has is to brighten your tone when you turn the volume pot on your guitar down,

No. With passive guitar signals, the only audible effect of the conditioning is to increase S/N (by effectively lowering the noise floor), specifically at higher frequencies.

It looks worse on the curve than it sounds even when the input level is relatively high.

See above. Were you to to prefilter a sweep so that its frequency content matches that of a guitar, then match levels, you would find that no self-limiting occurs.

I do believe however that people with good ears, hot pickups or active preamps, and who use bright clean tones could notice a difference in the sound of the front and rear inputs.

"Hot" passive pickups are never "hot" at high frequencies. The parameters that make them hotter - greater number of turns on the coils - also increase series inductance - and therefore reduce HF output - by the same amount as signal output is increased. Active pickups would be another matter, and that is why the rear input is different. Active pickups will not benefit from the "secret sauce" in the same way that passive ones will.

 

[AlbertA]

This is what I get using the same methodology and tools that you use Stephen/sampleaccurate (flat within 2dB window like Jay's measurements), Were you trying to control the input level with only the input1 knob?

 

[JKos]

Stehpen,
Perhaps a test you can run is to analyze the spectral content of your guitar then build a sweep which replicates that spectral content. Feed that sweep through your Axe-Fx and then compare the relative levels of the input sweep to the resulting output.

As mentioned above, a constant level sweep is by no means representative of an actual guitar or bass.

- John