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Topic: Question regarding gain and preamp settings (Read 11309 times) previous topic - next topic
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Question regarding gain and preamp settings

I just purchased a Behringer HA 4700 headphone amp, and am not really sure how to get the most out of it.

Right now I'm using FB2k, DSP's are Dolby Headphone>Noise Sharpening.

I have the preamp in foobar all the way down to 77dB, and it is all running through an M-Audio Transit at 24/96, and then through the Behringer Amp, into some Shure SE310's.

Since adding the amp I have stopped using the FB2k EQ and turned the preamp down to where it is now.

Everything sounds really great with the addition of the amp, however, this tends to be mostly towards the louder end of the spectrum.

When the volume on the amp is low, I have noticed some feedback.

This isn't that bothersome, as I tend to enjoy loud music anyways, but for the softer stuff it does get a tad annoying at times; i am now considering just bypassing the amp in those situations...

Anybody have any insight as to my setup, the preamp settings, and/or the feedback issue?

I would really appreciate some help from you guys.

Thanks in advance.

Question regarding gain and preamp settings

Reply #1 –
I don’t do any level adjustments in software, or elsewhere, on the computer. There is a volume control knob on the headphone amplifier and that works just fine. Why do you want to attenuate the signal in the media player?

Question regarding gain and preamp settings

Reply #2 –
It doesn't take much to drive my headphones, so if I were to leave the preamp at default, my output volume on the headphone amp would be limited to about a 2.

I was under the impression that lower preamp gain equated to greater dynamic range.  Is that not necessarily true?

I listen to a lot of experimental electronic with an absurdly wide dynamic range...

Question regarding gain and preamp settings

Reply #3 –
Quote from: audioslut512 on
It doesn't take much to drive my headphones, so if I were to leave the preamp at default, my output volume on the headphone amp would be limited to about a 2.

I was under the impression that lower preamp gain equated to greater dynamic range.  Is that not necessarily true?

I listen to a lot of experimental electronic with an absurdly wide dynamic range...

Where is the pre-amp located in your audio chain?  Are you talking about the pre-amp in your media player, on your soundcard? or somewhere else.

Generally speaking, you should only attenuate volume (negative gain) in your signal chain when it prevents clipping.

Question regarding gain and preamp settings

Reply #4 –
Quote from: benski on
Quote from: audioslut512 on

It doesn't take much to drive my headphones, so if I were to leave the preamp at default, my output volume on the headphone amp would be limited to about a 2.

I was under the impression that lower preamp gain equated to greater dynamic range.  Is that not necessarily true?

I listen to a lot of experimental electronic with an absurdly wide dynamic range...

Where is the pre-amp located in your audio chain?  Are you talking about the pre-amp in your media player, on your soundcard? or somewhere else.

Generally speaking, you should only attenuate volume (negative gain) in your signal chain when it prevents clipping.


I was talking about the preamp in foobar2000.  Why only to prevent clipping?

Question regarding gain and preamp settings

Reply #5 –
Quote from: audioslut512 on
Quote from: benski on

Quote from: audioslut512 on

It doesn't take much to drive my headphones, so if I were to leave the preamp at default, my output volume on the headphone amp would be limited to about a 2.

I was under the impression that lower preamp gain equated to greater dynamic range.  Is that not necessarily true?

I listen to a lot of experimental electronic with an absurdly wide dynamic range...

Where is the pre-amp located in your audio chain?  Are you talking about the pre-amp in your media player, on your soundcard? or somewhere else.

Generally speaking, you should only attenuate volume (negative gain) in your signal chain when it prevents clipping.


I was talking about the preamp in foobar2000.  Why only to prevent clipping?

Any further attenuation reduces resolution and dynamic range unnecessarily.

Question regarding gain and preamp settings

Reply #6 –
Audioslut(!),

You're probably fine, but let's think it through...

Most of your sources are probably 16-bit recordings. Few will use the full dynamic range available, but let's assume you have one somewhere that gets close.

Your "24-bit" sound card probably has a noise floor somewhere around the 15th to 20th bit level, sometimes frequency dependent.

Running at 77dB rather than 89dB (which = no change) is equivalent to dropping 2 bits (-6dB). ReplayGain will reduce the loudness of loud tracks, usually by an amount equivalent to dropping 1-2 bits. It probably won't reduce the loudness of any track quiet/dynamic enough to make full use of the 16-bits, so where it matters, you're unlikely to be dropping any bits at all - it might even increase the volume on such tracks, counteracting your pre-amp setting.

So, at worst, with a high noise floor on the sound card, a negative ReplayGain, and a moment in that recording that makes use of the full 16-bits, you are introducing audible noise.

At best, with a low noise floor sound card, a negative ReplayGain and no near-silent moments, or a 0 or positive ReplayGain, you're doing no harm at all. It would be objectively better if you didn't have the pre-amp so low, but you're not hitting a noise floor which is audible or measurable in the presence of the original signal, so the objections raised by others in this thread are academic.


I'd be far more worried about this "feedback" at low levels. I'm not sure what you mean (I can't imagine how it is really feedback), but this certainly shouldn't happen. At low levels (i.e. with the analogue system gain turned down), I'd expect near-silence to be eerily silent.

Cheers,
David.

Question regarding gain and preamp settings

Reply #7 –
Quote
When the volume on the amp is low, I have noticed some feedback.
  I assume this is noise, rather than feedback.*

The challenge is to maximize the signal-to-noise ratio.

There will always be some noise coming out of the soundcard.  When you reduce the volume with software, the output-noise remains constant and your signal-to-noise ratio is degraded.  If you then amplify the signal (with your headphone amp) you will also amplify the noise.

If you reduce the volume at the headphone amp, you will reduce the signal and the soundcard-noise together. 

The headphone amplifier will generate some noise internally too.  Some or all of this noise may not be reduced when you turn-down the amplifier's volume control.

There will probably be some noise leaked-into the soundcard before the volume control stage, and that part of noise will be reduced when you reduce the soundcard-volume with software.

Since you can't control the noise generated by the electronics, the idea is to keep a strong signal through the whole chain...  as strong as possible without clipping until the last stage.  Since it's impractical (and bad design for other reasons) to put a high-power potentiometer at the speaker-output, volume control is usually done at the preamp output (the last practical point).

Quote
I was under the impression that lower preamp gain equated to greater dynamic range. Is that not necessarily true?
  Well...  it could reduce the noise contributed by the preamp and the noise fed into the preamp.  In general, a high gain amplifier is noisier than an equivalent low-gain amplifier.  And, if you turn-up a microphone preamp, you can usually hear some hiss.    But, that doesn't tell the whole story because you usually need the gain!  (You do want to avoid reducing gain at one stage, and then adding-back gain at another.)    If you set the gain at zero, you've got zero dynamic range!  The high-end of the dynamic range is set by the signal level (or the clipping/distortion limit).  The low-end is limited by noise.



* Soundcard noise can be quite different from "traditional" hiss & hum.  Inside a computer there are lots of oscillators & signals that can leak into the soundcard, or if you amplify a very-low level digital signal, you may notice quantization noise.

Feedback is the loud squeal (oscillation) you hear when a singer gets the mic too close to the speaker.  The sound "feeds-back" into the microphone from the speaker.  Feedback is almost always full-power, because the sound gets amplified each time it passes through the "loop" until the power amp clips.  (If there is a delay, you will get an echo.)  It is possible to get feedback inside your soundcard....  I forget exactly how at the moment.... but this is also a full-power oscillation.

Question regarding gain and preamp settings

Reply #8 –
Quote from: 2Bdecided on
Audioslut(!),

You're probably fine, but let's think it through...

Most of your sources are probably 16-bit recordings. Few will use the full dynamic range available, but let's assume you have one somewhere that gets close.

Your "24-bit" sound card probably has a noise floor somewhere around the 15th to 20th bit level, sometimes frequency dependent.

Running at 77dB rather than 89dB (which = no change) is equivalent to dropping 2 bits (-6dB). ReplayGain will reduce the loudness of loud tracks, usually by an amount equivalent to dropping 1-2 bits. It probably won't reduce the loudness of any track quiet/dynamic enough to make full use of the 16-bits, so where it matters, you're unlikely to be dropping any bits at all - it might even increase the volume on such tracks, counteracting your pre-amp setting.

So, at worst, with a high noise floor on the sound card, a negative ReplayGain, and a moment in that recording that makes use of the full 16-bits, you are introducing audible noise.

At best, with a low noise floor sound card, a negative ReplayGain and no near-silent moments, or a 0 or positive ReplayGain, you're doing no harm at all. It would be objectively better if you didn't have the pre-amp so low, but you're not hitting a noise floor which is audible or measurable in the presence of the original signal, so the objections raised by others in this thread are academic.


I'd be far more worried about this "feedback" at low levels. I'm not sure what you mean (I can't imagine how it is really feedback), but this certainly shouldn't happen. At low levels (i.e. with the analogue system gain turned down), I'd expect near-silence to be eerily silent.

Cheers,
David.



Ok David,

Great response, it's starting to make a bit more sense to me now

So is it best to have the gain set right beneath the threshold at which clipping would occur?

I have read a lot of posts on foobar preamp settings in which people were saying that the 89dB default was just an arbitrary number (and that it used to be 83dB), for the purposes of replaygain, and that some thought 89dB was too high for uncompressed/dynamic tracks, yet it was ok for compressed pop and such...

As far as the "feedback", I was referring to a sort of humming noise I noticed when there would be a period of silence between tracks and/or at low volumes.

I have sort of remedied the problem, by just moving some wires away from each other, which seems to have reduced that humming, though I just can't seem to figure out what is causing the interference.

Are there some general guidelines for wiring and such as to prevent this sort of interference or is it just trial and error?


Best,

A.S.

Question regarding gain and preamp settings

Reply #9 –
Quote from: audioslut512 on
Are there some general guidelines for wiring and such as to prevent this sort of interference or is it just trial and error?

Keep audio signal cables separated as far as possible from the AC power cords, and when they need to be near one another, never run them in parallel but rather perpendicular to each other.

Also, when running audio cables from one AC operated device to another, make sure that both devices are properly grounded and plugged into the same circuit.

Question regarding gain and preamp settings

Reply #10 –
Quote
I have sort of remedied the problem, by just moving some wires away from each other, which seems to have reduced that humming, though I just can't seem to figure out what is causing the interference.
  Weird...  With short-shielded cables, you really shouldn't have that problem. 

If you have economy cables, you might need to get some "100% shielded" cables.  They don't have to be expensive "audiophile" cables, as long as they are fully-shielded.

If you have a long cable run, there may be no solution (other than moving the cables around).

Professionals avoid this problem by using balanced (and shielded) connections.  Your professional headphone amp DOES have balanced inputs, but your soundcard probably doesn't have balanced outputs.  (I've never seen balanced connections on any "home audio" equipment.)
 

Question regarding gain and preamp settings

Reply #11 –
Quote from: audioslut512 on
I have read a lot of posts on foobar preamp settings in which people were saying that the 89dB default was just an arbitrary number
I've seen one person saying something silly like that...

Quote
(and that it used to be 83dB)
almost true, but misleading in thsi context: - the tag standard was originally going to be 83dB, and most players would boost the result by 6dB - this was rapidly changed to tagging for 89dB and most players leaving it at that.

Quote
some thought 89dB was too high for uncompressed/dynamic tracks, yet it was ok for compressed pop and such...
yes, that can be true.


It's easy to get a handle on this though. Find a track that you think is really dynamic, and take a look at the ReplayGain values. (TrackGain or AlbumGain - whichever you're using). If they are positive, and if the track already peaks at 100% (0dB FS), then applying them as-is will cause clipping. You would either need to lower the pre-amp, or enable clipping prevention, to prevent this. Clipping prevention will make that track sound quieter than other tracks (i.e. ones where it doesn't kick it). Lowing the pre-amp will make all tracks sound (equally) quieter. Pick whichever compromise suits you best. Most people who know about this and have albums where this is an issue will do a bit of both - put the pre-amp down to 83dB, and enable clipping prevention to catch anything this doesn't solve (very rare!)


btw, just reducing the pre-amp where it isn't needed will, objectively, reduce the dynamic range - not increase it.

Hope this helps.

Cheers,
David.

Question regarding gain and preamp settings

Reply #12 –
Quote from: 2Bdecided on
Quote from: audioslut512 on
I have read a lot of posts on foobar preamp settings in which people were saying that the 89dB default was just an arbitrary number
I've seen one person saying something silly like that...

Quote
(and that it used to be 83dB)
almost true, but misleading in thsi context: - the tag standard was originally going to be 83dB, and most players would boost the result by 6dB - this was rapidly changed to tagging for 89dB and most players leaving it at that.

Quote
some thought 89dB was too high for uncompressed/dynamic tracks, yet it was ok for compressed pop and such...
yes, that can be true.


It's easy to get a handle on this though. Find a track that you think is really dynamic, and take a look at the ReplayGain values. (TrackGain or AlbumGain - whichever you're using). If they are positive, and if the track already peaks at 100% (0dB FS), then applying them as-is will cause clipping. You would either need to lower the pre-amp, or enable clipping prevention, to prevent this. Clipping prevention will make that track sound quieter than other tracks (i.e. ones where it doesn't kick it). Lowing the pre-amp will make all tracks sound (equally) quieter. Pick whichever compromise suits you best. Most people who know about this and have albums where this is an issue will do a bit of both - put the pre-amp down to 83dB, and enable clipping prevention to catch anything this doesn't solve (very rare!)


btw, just reducing the pre-amp where it isn't needed will, objectively, reduce the dynamic range - not increase it.

Hope this helps.

Cheers,
David.


So i apply replay gain to all my tracks and leave the preamp at 89dB, yet some tracks are peaking at -3 or -4dB, does that mean I should boost the preamp gain to get those tracks closer to 0dB?  Do I have other options?

Question regarding gain and preamp settings

Reply #13 –
Quote from: audioslut512 on
So i apply replay gain to all my tracks and leave the preamp at 89dB, yet some tracks are peaking at -3 or -4dB, does that mean I should boost the preamp gain to get those tracks closer to 0dB?  Do I have other options?

Peak values are not a good measure of how loud the music is. If you forced all of the tracks to have equal peak values then they would most certainly not sound equally loud.

By the way, you should also explore the concept of album gain vs. track gain. Some tracks are intentionally louder than others and you may want to preserve that.

Question regarding gain and preamp settings

Reply #14 –
Quote from: pdq on
Quote from: audioslut512 on

So i apply replay gain to all my tracks and leave the preamp at 89dB, yet some tracks are peaking at -3 or -4dB, does that mean I should boost the preamp gain to get those tracks closer to 0dB?  Do I have other options?

Peak values are not a good measure of how loud the music is. If you forced all of the tracks to have equal peak values then they would most certainly not sound equally loud.

By the way, you should also explore the concept of album gain vs. track gain. Some tracks are intentionally louder than others and you may want to preserve that.


I've been using album gain, is that that the best way to preserve intentionally loud tracks?

I just picked up some monster cables, and the humming sound is completely gone!  So much for Radio Shack's "Gold Series", should have seen that coming i guess...