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Going below 75db with mp3gain?
zeitfliesst
post Jun 21 2012, 00:42
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I've recently bought an amp for my IEM's, which are the most sensitive ones I've used so far. In order to get comfortable volume levels, I've brought down my entire mp3 collection to a volume level of ~72db, which I found is 3db lower than the minimum "allowed" by mp3gain (when you enter anything below that it resets to 75db). Is this going to affect my mp3 files in any way that will degrade its sound quality? I've listened to the files and they don't sound different, but just wanted to make sure if this is a safe thing to do...
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Canar
post Jun 21 2012, 00:45
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You had: Device -> Headphones
You now have: Device -> Amp -> Headphones

Was the amp really necessary? You're gaining no audio quality from it. Amping IEMs might even damage them or your ears. They're designed to run with very little electricity, as you'd expect for something that is inserted into the ear canal.


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zeitfliesst
post Jun 21 2012, 00:48
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Well, I think that is really a subjective thing, and not the point of this thread. I've seen plenty of people on head-fi using IEM's with portable amps, and I don't want to argue about whether there's a benefit in doing that or not. If others could try and answer my original question that would be great. Thanks.

QUOTE (Canar @ Jun 20 2012, 17:45) *
You had: Device -> Headphones
You now have: Device -> Amp -> Headphones

Was the amp really necessary? You're gaining no audio quality from it. Amping IEMs might even damage them or your ears. They're designed to run with very little electricity, as you'd expect for something that is inserted into the ear canal.

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mjb2006
post Jun 21 2012, 04:43
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The 75 dB limit is being imposed by the GUI. The command-line app that the GUI is invoking doesn't have this restriction.

Sound quality is unaffected by applying gain reductions, except in a very unusual situation which isn't worth explaining here.
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zeitfliesst
post Jun 21 2012, 05:28
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Ah I see. Thanks for the confirmation. I've once accidentally applied a gain that was really low (don't remember the exact number) and it totally messed up the file for good. This got me worrying that I might have been close to that minimum volume "allowed" if there is one.

QUOTE (mjb2006 @ Jun 20 2012, 21:43) *
The 75 dB limit is being imposed by the GUI. The command-line app that the GUI is invoking doesn't have this restriction.

Sound quality is unaffected by applying gain reductions, except in a very unusual situation which isn't worth explaining here.


This post has been edited by zeitfliesst: Jun 21 2012, 05:28
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probedb
post Jun 21 2012, 08:45
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QUOTE (Canar @ Jun 21 2012, 00:45) *
Was the amp really necessary? You're gaining no audio quality from it. Amping IEMs might even damage them or your ears. They're designed to run with very little electricity, as you'd expect for something that is inserted into the ear canal.


Many, many people have headphones amps for IEMs. Generally people know how to use the volume control which is the only thing that could actually do anything. You could do the same without a headphone amp, assuming your device has an amp capable of producing the necessary power.

To the OP, I'm a little unsure of how you can't turn the volume below something that's uncomfortable for your ears which seems to be what you're saying?
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2Bdecided
post Jun 21 2012, 09:54
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QUOTE (probedb @ Jun 21 2012, 08:45) *
To the OP, I'm a little unsure of how you can't turn the volume below something that's uncomfortable for your ears which seems to be what you're saying?
Yes, there seems to be something missing from the original question, because the obvious answer is the volume control!

It's a rare album where you need less than 83dB target level to prevent clipping. In the modern pop world, even 89dB is considered conservative by some!

By using 72dB as a target, with a typical compressed pop master (which needs -10dB to hit 89dB) you'll reduce the gain by 27dB compared to the original - or looking at it another way, you'll chop the bottom 4-5 bits off the audio signal. Many people assume this is a really terrible thing to do - but that probably means they've never tried it - compressed pop music sounds identical with only 12-bits left (except during the fades and any quiet moment, if you turn it up during those parts). 10-bits is often sufficient. Look at what LossyWAV does.

Stereotypically, the kind of people who think it's OK to use 12-bit audio, and the kind of people who think apparently good headphone outputs benefit from adding an amplifier, sit at opposite ends of the audiophile spectrum. This doesn't stop them both being right in some situations.

Cheers,
David.
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zeitfliesst
post Jun 21 2012, 13:47
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I was a bit unclear in my original post, but the reason I had to reduce the volume on my mp3 files (the source) is because the amp had too high of a gain and therefore even the minimum volume required to get out of channel imbalance was too high for me.

2Bdecided// Thanks for that info, but I still don't quite get how reducing the volume gain will affect the sample size as you have said. Please help me understand this concept. So would applying a positive gain (eg. back to 89db) return the files back to 16-bit? That doesn't quite make sense because mp3gain claims to be a lossless way of changing volume.

This post has been edited by zeitfliesst: Jun 21 2012, 13:48
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onkl
post Jun 21 2012, 14:02
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Instead of messing with your files, why not adjust the software volume? You can either turn down the volume of your player or the operating system.

This post has been edited by onkl: Jun 21 2012, 14:03
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zeitfliesst
post Jun 21 2012, 14:39
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OK. I guess I haven't been clear enough. I'm using a line-out from the ipod, so I cannot control the volume on the player itself. Only with the amp.

QUOTE (onkl @ Jun 21 2012, 07:02) *
Instead of messing with your files, why not adjust the software volume? You can either turn down the volume of your player or the operating system.

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Canar
post Jun 21 2012, 15:09
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QUOTE (zeitfliesst @ Jun 20 2012, 16:48) *
Well, I think that is really a subjective thing
Not in the slightest.

QUOTE
and not the point of this thread.
It's absolutely the point of the thread; without it there's no problem.

QUOTE (zeitfliesst @ Jun 20 2012, 16:48) *
I've seen plenty of people on head-fi using IEM's with portable amps, and I don't want to argue about whether there's a benefit in doing that or not.
So go back to Head-fi and ask this. We're going to call you out on the problems you're facing. Just because there are idiots doesn't magically make idiots right.

There is no point to this additional amplification. The amp provides nothing more than additional distortion and non-linearity. It's not like it can wave a magic wand and magically restore fidelity from your original source. It does nothing whatsoever except decrease overall fidelity and increase gain. Expecting people to pass over obvious, glaring, objective faults in your setup, especially when over-amplification is your whole problem is asinine.

Instead of using iPod line out, why not just use your iPod headphone out? It's pretty high-powered, has its own gain control, and is not an intermediate step causing further loss of fidelity.

What's more, as the whole damn thing is a portable audio setup, this restores actual portability, instead of carrying some half-baked headphone amp around that does nothing but give you problems. Don't be a stupid hipster.

This post has been edited by Canar: Jun 21 2012, 15:16


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probedb
post Jun 21 2012, 16:06
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QUOTE (zeitfliesst @ Jun 21 2012, 13:47) *
I was a bit unclear in my original post, but the reason I had to reduce the volume on my mp3 files (the source) is because the amp had too high of a gain and therefore even the minimum volume required to get out of channel imbalance was too high for me.


Then ditch the amp, it's obviously causing the issues as Canar says.

What IEMs, amp and device are you using and maybe we'll be able to suggest something useful. You shouldn't need to use anything other than default RG.

I have UM3x and they're very sensitive and have no issues using either a Sansa Clip+ or a FiiO E7 USB DAC/amp. I would say the amp is a very big problem.
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zeitfliesst
post Jun 22 2012, 00:07
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Canar:

Well, a little bit more polite and I would have actually thanked you for that. It's crazy how people get so aggressive over nothing.

All I wanted help with was the question about mp3gain. You can call me a stupid hipster all day long, but you still haven't addressed my question about mp3gain.

probedb:

Well, I had no problems over volume control with my RSA Mustang amp before, but the new one I just bought (JDS c421) has a slightly higher gain than I thought. Maybe I will ditch it, maybe I will not, but I'd still like clarification on whether reducing gain with mp3gain will damage the quality of files (as 2Bdecided mentioned, does it reduce sample size and why? Is it reversible?)

This post has been edited by db1989: Jun 22 2012, 00:18
Reason for edit: merging posts and replacing both unneeded full quotes with names (and please do not bottom-quote when you have to)
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skamp
post Jun 22 2012, 09:03
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The only upside to using an external amp that I can think of, is having a 0 ohm output impedance with low impedance balanced armature IEMs that suffer from wild frequency response variations when presented a higher output impedance. Other than that, you're amplifying a signal, giving more voltage/power, to IEMs that in fact require less of it than some other headphones! The C421 has a minimum gain of +7.2dB, it's no wonder you're having problems!

I guess you drank the Head-Fi kool-aid that suggests that external amps have some magical (never measured!) properties that always makes sound quality better. I don't blame you: it's repeated so much post after post and thread after thread that it's only natural to start believing it. Well, amps have a tangible purpose, like I said: to amplify the signal. And there's nothing magical about it. In your case, it's obviously degrading sound quality, so I suggest you find another solution.

As for mp3gain, you can losslessly undo changes with the -u switch.

This post has been edited by skamp: Jun 22 2012, 09:10


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db1989
post Jun 22 2012, 09:30
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QUOTE (zeitfliesst @ Jun 22 2012, 00:07) *
I'd still like clarification on whether reducing gain with mp3gain will damage the quality of files (as 2Bdecided mentioned, does it reduce sample size and why?[…])
Not of files. It will reduce the effective bit-depth of the audio that is output – but, as 2Bdecided mentioned, this may well be inaudible. Still, that’s another good, if perhaps theoretical, reason not to add unnecessary amplification when you don’t have to.

QUOTE
Is it reversible?
Yes. All MP3gain does is to add a field to the MP3 file that instructs the player to scale it by ReplayGain’s computed gain reduction/increase, rounded to the nearest 1.5 dB. This can be reversed simply by reverting the scale-factor to zero.
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2Bdecided
post Jun 22 2012, 10:28
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QUOTE (db1989 @ Jun 22 2012, 09:30) *
Yes. All MP3gain does is to add a field to the MP3 file that instructs the player to scale it by ReplayGain’s computed gain reduction/increase, rounded to the nearest 1.5 dB. This can be reversed simply by reverting the scale-factor to zero.
Not quite - it changes a scalefactor that's already present as part of the mp3 format. You reverse the change by returning it to its original value in each frame. Which is trivial, as long as you know what gain you applied to start with.

The loss of resolution is simply that most mp3 decoders output output 16-bit fixed point linear PCM without dither. If you reduce the volume within the file, then some of the information now falls below the least significant bit, and is either quantised to a square wave or lost entirely (depending on how it happens to hit the quantisation steps). Files that ReplayGain attenuates don't usually have any quiet information like this. If they do, and you turn up the volume to hear them, they won't be there. This is usually an irrelevance, but going down to 72dB target could create a real audible problem with some tracks IMO - especially, say, a dynamic classical recordings, ReplayGained in album mode, but listening to the quietest track/movement with the volume cranked right up. It's within the bounds of possibility that you'd hear a difference. Someone else will have to do looking to see if an example can be found in practice!


Anyway, the use of this amplifier in this way isn't improving your listening experience! Audible inter-channel imbalance?! Taking your audio files effectively down to 12-bits?! This is madness. If the output impedance of your mp3 player is an audible problem with your headphones, you need a buffer with an exceptionally low impedance output, or a better/different mp3 player, or different headphones. Or if you must use the line output, an amplifier that gives a full range of attenuation and amplification (if/when needed).

Cheers,
David.
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db1989
post Jun 22 2012, 13:26
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Thanks for the corrections and clarifications, David!
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