Will changing gain affect frequency response?

This article may offer some insights:  (http://ehomerecordingstudio.com/fletcher-munson-curve/)

I suppose looking at a Fletcher-Munson graph may be a good idea, as well: (https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves)

In addition to the famous Fltetcher-Munson loudness curves, you don't talk about whether you are running a tube preamp or not.

Tube preamps are sometimes quite sensitive to this, and it has to do with the impedance changing as the resistance in the volume changes. The better tube preamps have buffer stages or volume control configurations that prevent this, but not all.

Best,


Erik

Thanks for the replies so far.

The tube pre-amp (2-6H30s, 1 EZ80 rectifier) is what has a -10 db option. The effect from altering the phono pre gain setting was "heard" in playback using a solid state integrated amp (no tubes involved in that chain).

I’ll check info at those links.

Take away so far, however, is there might be an objective basis for a difference in tone...not just imagination.

hahaha...okay. Started reading Rodman's link.  Didn’t know anything about the Fletcher Munson curve. So, it sounds like there is a well known linkage between volume and perceived frequency response - a psychoacoustic effect, I guess. But let me repeat, what I’m asking about is what might explain an effect on frequency response when the volume at the listening position has been adjusted down ("normalized") to compensate for the increase in gain. Is the F/M response relevant in that situation?

Right,  I wouldn't call F-M curves "psycho-acoustic" as your knowledge or lack of it has no bearing on the perception. It's more of an ear-sensitivity issue. 

If you remember equipment with a  "loudness" switch, or dial, they were meant to compensate for this known effect, and some speakers are deliberately tweaked along those lines to make it seem like you hear more detail at lower volumes.  Well, you DO hear more detail, but it also means at higher volumes you get exaggerated treble and/or bass. :)

Best,


Erik

Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound (including speech and music). It can be further categorized as a branch of psychophysics.

Loudness is the characteristic of a sound that is primarily a psycho-physiological correlate of physical strength....

Hi Eric - I'm using psychoacoustic as defined above applied to the perception of loudness quantified by "phon".  Because of how we perceive sound, varying dBs are required to support a constant level of loudness across a range of frequencies.  Each F/M curve is dB (Y) as a function of frequency (X) for one level of loudness (constant phon). 

I suspect what I'm hearing (if real!) might be a function of electronics, not a function of the "hearing response" (one aspect of which the F/M curves are describing).    

Well, I'm in no way arguing F-M. Of course, they are old, and may need updating, but the principle has been around and used for a long time. :)

Best,

Erik

Hello again, Erik.  Thanks for your time considering this.  I'm not arguing the F/M curves either....more a case of not sure they explain what I think I hear when gain is increased but volume reset to the original level.  

Ghosthouse, yes, you're right that the Fletcher-Munson Effect will not cause a change in perceived tonal balance if the volume at the listener's ears remains constant.

Regarding your original question, yes it does seem conceivable that changing how the overall system gain is distributed among the various circuit stages that are in the signal path could affect perceived brightness.  Although without knowing the details of each of the designs that are involved a more specific explanation would be speculative at best. 

For example, Atmasphere has pointed out in a number of past threads that very small amounts of certain harmonic distortion components (e.g. the 5th, 7th, and 9th harmonics) can affect perceived brightness.  Changing the signal levels that are processed by the various gain stages that are involved could conceivably affect the degree to which those distortion components are generated.  Erik mentioned another example, which is that impedances might change, depending on the specific designs.  If the output impedance of a component were to change significantly, and is relatively high, its interaction with cable capacitance could affect treble response to a perceivable degree.  And it seems conceivable that changes in impedance at internal circuit points could also affect the treble, depending on the specific designs. 

Best regards,
-- Al
 

Thanks, Al.  Does sound like there are few possible hardware-based explanations for what I thought I heard.  

Seems I missed(spaced) the part where you brought the volume back down, at the listening position.    Kinda obviates Fletcher-Munson from the conversation(sorry).

It's like a glass of water, if you fill up all the way, you will have to limit yourself on the speed of carrying that glass of water because not enough 
'headroom' left to keep water stable inside.
If you do not fill up, than you might be still thirsty and desire more water in your glass. So the goal is to reach sufficient level of water so it doesn't spill and it fills you up.

czarivey
3,215 posts
09-13-2016 12:10pm
It's like a glass of water, if you fill up all the way, you will have to limit yourself on the speed of carrying that glass of water because not enough 'headroom' left to keep water stable inside. If you do not fill up, than you might be still thirsty and desire more water in your glass. So the goal is to reach sufficient level of water so it doesn't spill and it fills you up.

Maybe substitute the word vodka for water.

I can, but prefer cognac to all spirits :-)

Rodman - Absolutely no need to apologize. Those Fletcher Munson curves were new to me so you added to my little store of audio knowledge. Thanks for taking the time.

Czar - Interesting analogy.  I think I get your point applied to gain settings.

NOT talking about increasing the volume at the listening position

Increasing the gain by moving the jumper to the highest position

(keeping the volume the same at the listening position)
In some cases this gain change in a preamp/amps/cdp/dacs with links can be done buy a change in the negative feedback ratio loop.

And if you change the negative feedback, you change the things like the distortion, frequency response, stability, damping factor, slew rate and many more factors.
(In most cases the less the negative feedback, the more gain you have)

So what I’m saying is the "brightness" thing your hearing may vey well be the change in one of all of these factors, if these links apply to the negative feedback.

I know in a few Cary/Wadia dac/cd players it was done this way to have the user use the digital domain volume control used only it the top quarter of full, so the risk of "bit stripping" was minimalized.
Cheers George

In addition to how changing the gain of a preamp can change sound due to nonlinearity of the gain control, another thing to consider is where you achieve the gain.  For instance, I can change the gain on my phono preamp as well as on my main preamp.  I have tried it both ways and using the main preamp for increased gain sounds better than increasing the gain in my phono stage.

This discussion poses a question in regards to the Preamp-Amp gain/volume control. Should I run the amps [Mcintosh MC 60s] full out with the gain controls available on each amp and use a lesser level of volume on my preamp,[Zesto Leto tube pre]? Does trimming the gain on the amps give me less headroom when listening at higher volumes?

The output impedance of the Preamp is relatively low 150-250 Ohms to the input impedance of the amps which is 500K ohms. The preamp has two settings for gain, set internally, of 3 db and 12 db and came to me set at 3 db. I have very efficient speakers so the headroom of the amp and pre is sufficient either way. I rarely have the volume on the pre at 12, more at 10-11 max with the gain on the amps maxed out.

I ask this because I do fight brightness a bit and would like to optimally control the tone of the system towards a bit more mellow direction. 

The preamp has two settings for gain, set internally, of 3 db and 12 db and came to me set at 3 db.

Back to my first post, which everyone overlooked, how is this reduction achieved? Is it via the feedback network??
If so, this can influence the tonal quality, of where these gain setting positions are used, and they have nothing to do with the vc knob being high or low physical position for the same given volume.

Cheers George

I second what rlawry says above about the non-linearity of the particular gain control, versus that of the volume control itself in particular.

Almost as an aside, Steve Deckert of Decware advocates introducing an extra gain stage control inserted after the source, in addition to the one at your amp (ZBOX). This allows you to do some "gain riding" as he calls it, letting you either turn up the gain going out of your source while also turning the gain down going into your amp....or vice versa. I haven’t tried it that way (yet), but he says that increasing the source output gain while lowering the amp input gain, definitely changes the overall character of the sound...in the right adjustment zone, he says the sound in that instance is much more dynamic. Presumably you can take this idea too far and it may begin to deteriorate the sound in some other regards the further your adjustments go, but his point is that you have a choice of what sounds best to you. If this arrangement produces that result, then perhaps it is not hard at all to accept that you are hearing, ghosthouse, a slight difference in tonal response in your set up (and that Al would be correct by way of what he has already pointed out, as usual, but I defer to Al and others on most matters ee).

Here is the ZBOX link which has a description and a link to the owner’s manual: www.decware.com/newsite/zbox.htm Steve makes mention of both impedance and frequency response.

Claims are a bit out there.
How can a tube buffer with 1000ohms output impedance, be a better impedance match than a 100ohms or even less output impedance source with it's own VC, into say the low 10kohm load  of one of the Pass Labs poweramps? 
And this 1000ohms output impedance will be even higher at lf as it's bound to be capacitor coupled!

Cheers George

You may well be right George. I have many unanswered questions about this unit and I'm certainly not here to vouch for it, as I've never seen one and don't intend to order one myself. When I go this route it will be with a simple, but good quality, distribution amp that I will be building myself since the Decware, nor any other unit that I could find, seemed to fit the bill for my particular setup. But, I wonder if any effect at all of the ZBOX will be at all evident with the distribution amp...even a small of it might be significant...not as any vindication at all of the ZBOX product (not at all recommending that ghosthouse go out and buy one), but simply pointing to the genuine impedance matching question, possibly.

George makes a good point that sonic consequences can particularly be expected if a gain change is implemented in a circuit via a change in the value of a resistor in a feedback loop.

Regarding Dentdog’s Zesto Leto, there doesn’t seem to be any indication at the website or in the manual as to how the gain change is implemented. (Although the manual states in bold-face type, in the paragraph dealing with the internal gain switch, that "due to high internal voltages there are no user adjustable switches, only authorized representatives can make these adjustments," and also states that the "warranty is void if the product has not been used in accordance with the instructions found in this owner’s manual.")

A schematic for the McIntosh MC60 can be found on the web and shows that its gain control is simply a resistive pot (potentiometer) used as a voltage divider and connected to the input through a capacitor.

As I see it the bottom line to Dentdog’s question, and to such questions generally, is that whatever sonic effects might result from changing how the overall gain is apportioned between components figures to be highly dependent on the specific designs that are involved. So in most cases the only way to find out is to try the various alternatives in the particular system, IMO.

Does trimming the gain on the amps give me less headroom when listening at higher volumes?

No, assuming that you don’t turn the gain controls on the amps so far down that you can’t drive them to full power (when and if that is required by the music and your volume preferences).

Regarding the ZBOX, it sounds like it uses the tube in a cathode follower configuration, and has an Alps pot at its input for gain control. It is described as using "large hi-end coupling caps," so perhaps the specified output impedance of "less than 1000 ohms" is conservative, even at 20 Hz. In any event, I would think that the key to its sonic effects, in addition to possibly allowing the gains of other components in the system to be optimized, is the mention that it "works by creating a starved voltage condition in the filament of the tube that in turn causes an increase in favorable harmonics and a decrease in objectionable distortion." Although I suppose the reduction in "objectionable distortion" may not really be a reduction, but rather a masking by the "favorable harmonics" that are introduced.

John ("Ivan"), thanks for the nice words.

Regards,

-- Al

I don’t believe this has been expressly mentioned. You can significantly effect how you "drive" your speakers by adjusting the gain and therefor the volume the speakers put out. I would be Very cautious however about over-driving the speakers and burning out the crossovers, blowing out the speaker surrounds or similar speaker or other damage. A friend of mine blew out the speaker surrounds of his speakers 3 times before he caught on that he had the gain adjusted too high. Adjusting the gain too high can also cause your equipment to "clip". The best setting for gain is just before your equipment begins to clip. This is the point at which you are driving your speakers and your equipment to the max - which is what you want to do- but you are not over driving it. I understand all of the discussion of volume and our perception that louder is better. Gain is really a different issue although it also results in variations in volume. Again, I would be most cautious about turning the gain up with careful consideration of the overall effect it is having on all of your equipment.

In addition to the points already made, an additional issue is that a room can sound brighter at higher volume levels!

I run into this all the time at audio shows where the rooms are hotel rooms that aren't built as well as rooms you might have in your house. At lower levels reflective surfaces such as windows and framed pictures might seem innocuous but if the room is driven too hard you might find it painful.

In a nutshell the room is at least 50% of the total system quality! I have lots of LPs and they have proven to be good room diffuser elements when neatly stored in their shelves (rather than stacked on the table beside by my turntable...). This is why there is a room treatment business.

One other thing that can affect tonality when the volume is increased is the effect of the volume control on the surrounding circuits. This usually affects tube preamps more than solid state. There is this thing called Miller Effect, which is the input capacitance of the amplifying device interacting with the outside world. It can affect frequency response! A classic example is a loss of high frequencies in the middle of the control (the impedance of the control interacts with the input capacitance of the tube or transistor) If you happen to use that part of the control a lot, turning it up past that point might make for more HF response.

This problem can be controlled by careful design.

I own a Mark Levinson preamp that has adjustments in gain for each input, the values are 0,6,12 and 18 db. My a amp is a McIntos h. I have played with the adjustable gain settings and my system comes to life with the preamp gain for my CD unit at 12db. 0 sounds bright, thin, lacking dynamics, 6 sounds much better but 12 really gives me the dynamics,  bottom end, much better mid-range, that the settings of 0,6 just cannot match, so gain does impact how your amplifier performs and it does big time.