Why your awesome IEMs sound bad from your iPod and what YOU can do about it!

[tbritton]

Quote:

Originally Posted by markopolo /img/forum/go_quote.gif I went throught this a while back. The Volume Adjustment within iTunes affects only final gain stage (post-EQ) and I believe is also bypassed by the iPod's line out. The only solution I've found is the MP3Gain/AACGain option previously mentioned, which analyzes and adjusts each individual file's "loudness" using the ReplayGain algorithm. The difference between these programs and the OPs method is that MP3Gain/AACGain stores the changes it made to each file as a tag (APE I believe), and is therefore reversible by a command within the program. As someone already mentioned, none of this would be necessary if Apple would just implement a pre-amp fader setting on the iPod as they do currently from within iTunes.

From what I can find on MP3Gain/AACGain, it is just a very smart front end for determiing what setting the Volume Adjustment tag should be set to for each file, and attains intelligent volume levelling that goes beyond peak normalization (which cannot always solve the problem that MP3Gain/AACGain does solve, adjusting songs so that perceived volume levels sound nearer to each other.) But that might not be the case - a check in iTunes of some songs processed by MP3Gain/AACGain still shows the Volume Adjustment slider set to zero - so, I'm not sure anymore what actual tag is being changed or read by the iPod, or where that reading is being applied among the amplifier stages.

This is a brilliant program, though! I played with it quite a lot this morning! It definitely works, and its analysis functions are pretty cool and spot places where the mp3 or aac file would clip, and allows you to fix the situation there. But I'm thinking it still only affects the final amplifier stages, and will not affect the pre-EQ levels so as to avoid gain-stage overloading by the EQ. (Although this poster seems to think it does help, but I can't find substantiation for his claims.) One very interesting application for this is reducing the Volume Adjustment tags so that you have to drive your iPod's amplifier gain harder to achieve loudness - which for most amps of this kind means increasing the current delivered to the headphone - loading it better for low impedance headphones, if I remember correctly. (Pushing the amp's final gain wide open while controlling volume by reducing the input level, if that's where this tag is doing its thing. I may have that all wrong, though, if this tag is really doing a "revision" of the numbers the volume control on the unit is doing... just minusing some amount from the manual setting...)

I had already ripped all my CDs to Apple Lossless as archives and created AAC 256 versions for my laptop and iPod. I may simply re-create the lossy/compressed versions in the laptop, as my experiments on the AAC 256 going to a LAME Extreme preset sounded excellent. I think this "Volume Quieten" DSP in dbPowerAMP may be a good workaround, for taking the lossless files and downsizing them, while applying this -2 dB adjustment on-the-fly. I can tell you, it has made all the difference in the sound of EQ'd Joe Satriani! 'Twas pure gleck! Using "Jazz" EQ setting now and it sounds great!

I am going to look more into the ReplayGain item you mentioned and these cool front ends and try some test runs. What it does, it is the best at! Thanks for the information! Still want to be clearer about what amplification this is actually altering, since it does not actually alter the file in any other way other than to add these Volume Adjustment tags in a very intelligent fashion. It may be doing more, though. More research...

Terry

 

[tbritton]

OK, according to this thread at Hydrogenaudio, http://www.hydrogenaudio.org/forums/...topic=24527&hl, mp3Gain and AACGain (both being implementations of the ReplayGain algorithms) affect volume settings of the actual few-millisecond-long individual blocks of the mp3 file, so it is an internal adjustment to the mp3 (or aac) file itself, and so, said volume adjustments are decoded directly by the player when reading the file, before entering any amplifier stages at all. The upshot is that using this program to reduce the overall volume sends a lowered signal to the fixed-preamp EQ in the iPod, and eliminates the problem of that EQ's output then overloading the input stages of the final amplifiers downstream.

The tags these programs write are apparently only for undo purposes.

That's right - the changes you make are entirely undo-able!

There are some problems that are raised in the above-mentioned post concerning these "undo" tags causing older versions of foobar2000 as a media player to ignore the id3 tags in favor of the APE format tags that hold the undo information, but workarounds are listed in the above post for people using foobar2000 who have "lost" the id3 tag info. (again, not really lost, only ignored...) These problems no longer seem to exist in current editions of foobar.

I used a setting of 83 dB that allowed me to pump my both my Nano's and laptop's amp to 8-ish or 9-ish and maximize their power loading on my low impedance headphones. It is making these smallish amps work fine with Shure E4c and Ultrasone Proline 750s, as well as with my "portable" phones like the Portapros and Sennheiser PCX-250s. (Coincidentally, that was the program author's original default, though that has been raised to 89 dB in current editions. For power-loading/impedance-matching purposes, 83 should work better.)


This should result in a very clean and distortion-free output from even these little 10 mW headphone amps. The added benefit is that this blows Apple's Sound Check out of the water. Be certain to turn Sound Check off on your iPod or in iTunes for playing files you've converted using either mp3Gain or AACGain.

BTW - get mp3Gain from here (This is all you need if you only intend to work with mp3 formats)

Then get AACGain from here near the bottom of the page (this is a direct link to that file)

If you intend to use the AACGain with this frontend: Go to your Program Files folder and inside the mp3Gain folder, change the name of mp3gain.exe to mp3gainOrig.exe to keep it for using with mp3s at another time, and then change the name of AACGain.exe temporarily to mp3gain.exe instead so the front end will find it.

The help files are very useful that come with the program. Experiment and tell us what results you got from it. Thank you, Markopolo for drawing my attention to these programs.

I hope this is of huge benefit to everyone who used to hate the iPod's unamped EQ sound! It definitely has improved matters, plus added the fringe benefits of levels controlling my tunes.

Terry

 

[tbritton]

I decided to check this post's assumptions and concepts with the folks over at hydrogenaudio.com. If you would like to follow that discussion, it takes place here:
http://www.hydrogenaudio.org/forums/...howtopic=51344

I hope this works for people!

Also, I'd like to acknowledge that the mp3gain solution, while elegant and what I myself am choosing to do, does not itself address the OP's original desire, which was to produce LOSSLESS final output. For that application, the earlier post suggesting using dbPowerAMP and its "Volume Quieten" DSP is still a better and more appropriate solution. There may be other solutions that can be used during the CD extraction stage, perhaps ripping via EAC, but I have only spotted hints here and there that such may be possible with Apple Lossless as a final output destination.

Terry

 

[tbritton]

I was hoping for some feedback on this topic and other ideas, so I've bumped this thread a little.

Terry

 

[IPodPJ]

Quote:

Originally Posted by tbritton /img/forum/go_quote.gif I was hoping for some feedback on this topic and other ideas, so I've bumped this thread a little. Terry

Hi Terry,

Thanks for taking such an interest in my thread.
I just went over to your thread on hydrogenaudio.com regarding this thread. Boy, those people are really technical over there, and quite knowledgeable, too.

I was quite taken by those RMAA results in regards to 16ohm vs. 32ohm. I can't believe the THD and SNL ratings are that shockingly different!!!

This clipping problem is related to the iPod's EQ most likely, and not to the resistance of the Super.Fi 5 pro. It is interesting that Apple used a hardware EQ in the 5th gen when all previous generations used software.

Note that the SF5pro is rated at 26ohm@1kHz. The Triple.Fi 10 pro is rated at 32ohm@1kHz. Aside from the EQ problem (which does not vary between the two IEMs since the clipping is an iPod hardware issue), I wonder if the sound quality of the SF5pro can be enhanced by adding an inline resistor. I'm not sure what ohm resistor would be of most benefit to the SF5pro, since I don't really know much about the technical aspects of impedance/resistance in general. The SF5pro wouldn't quite have the same noise and THD levels as a 16ohm IEM (as shown in the RMAA graphs) since it has 26ohm resistance, but judging by the extreme levels shown, I would venture to assume that adding additional resistance would be of benefit to the SF5pro (and any other IEM lower than 32ohm) when used with an iPod.

Also, what were the difference in ratings between the headphone out and the line out on the iPod? I'm not sure which the ratings were given for.

Thanks for your interest and help to the Head-Fi community!

 

[tbritton]

Quote:

Originally Posted by IPodPJ /img/forum/go_quote.gif Hi Terry, Thanks for taking such an interest in my thread. I just went over to your thread on hydrogenaudio.com regarding this thread. Boy, those people are really technical over there, and quite knowledgeable, too. I was quite taken by those RMAA results in regards to 16ohm vs. 32ohm. I can't believe the THD and SNL ratings are that shockingly different!!! This clipping problem is related to the iPod's EQ most likely, and not to the resistance of the Super.Fi 5 pro. It is interesting that Apple used a hardware EQ in the 5th gen when all previous generations used software. Note that the SF5pro is rated at 26ohm@1kHz. The Triple.Fi 10 pro is rated at 32ohm@1kHz. Aside from the EQ problem (which does not vary between the two IEMs since the clipping is an iPod hardware issue), I wonder if the sound quality of the SF5pro can be enhanced by adding an inline resistor. I'm not sure what ohm resistor would be of most benefit to the SF5pro, since I don't really know much about the technical aspects of impedance/resistance in general. The SF5pro wouldn't quite have the same noise and THD levels as a 16ohm IEM (as shown in the RMAA graphs) since it has 26ohm resistance, but judging by the extreme levels shown, I would venture to assume that adding additional resistance would be of benefit to the SF5pro (and any other IEM lower than 32ohm) when used with an iPod. Also, what were the difference in ratings between the headphone out and the line out on the iPod? I'm not sure which the ratings were given for. Thanks for your interest and help to the Head-Fi community!

It's an interesting topic!

The rolloff measurement was strictly concerning headphone outs. I'm not sure what would happen tapping a headphone directly from a line-out - it is expecting impedances in the meg-ohms at the input stages of an external amplifier.

I used the inline volume attenuator that came with my E4c's to test the repair suggested for this rolloff issue out (the E4c's are rated at 29 ohms), and did notice an improvement needing only a very slight volume reduction on the attenuator to make it become evident. I am going to buy two 46 ohm resistors and put them into a series adapter for further checking out. That will raise the impedance plenty high enough, probably higher than needed. May swap with some 27 ohm ones or less later. Resistors are very inexpensive, even for highest quality!

It is nice that the mp3gain/aacgain fix repairs the EQ distortion problem so neatly! I have my major collection ripped to Apple Lossless on the big PC, but have made high quality (256 kbps VBR) AAC copies on my laptop that I used aacgain upon and use to sync to my iPod Nano. No EQ problems now! And the "lossy" versions I find are plenty adequate for iPod use, or for playing via my laptop's soundcard and headphone jack. It amazes me that I have my entire CD collection on my laptop to listen to, and still have plenty of room for Photoshop/Adobe Creative Suite and lots of huge images (for work)!

The PC plays over high end speakers (or my Ultrasone Proline 750s) via a high end recording studio quality audio interface, and I have plenty of hard drive space reserved for my music collection there, so Apple Lossless is the favored archiving method, and naturally sounds as good as the CD! My home system, needless to say, does not have an EQ distortion problem, so no mp3gain/aacgain fix needed there! I use a volume leveller plugin in my playback program for that issue to be handled when I feel a need, and needn't change the files themselves.

I chose the 256 kbps setting in iTunes AAC for the iPod/laptop versions because it allowed VBR (variable bit rate), which does not alter the sound character, but only alters the bitrate to "fit" the audio content being compressed, according to the folks at hydrogenaudio, and thus works very well at keeping file sizes even smaller. The 320 kbps setting in iTunes does not allow VBR. (As far as I remember, Apple Lossless uses VBR automatically by default, and it is a lossless format, so that helps to substantiate that VBR itself does not lose anything sound-quality-wise in the translation.)

With the combo of the 256 kbps files and the compensation/reduction in volume made via mp3gain/aacgain to gain-stage match the EQ, and a little inline resistance to fix my Shure E4c's impedance matching issues, I have the best sounding iPod Nano one can accomplish without using an outboard amplifier!

I'm not entirely happy with the series-resistance fix, as it responds to the output capacitors in the Nano acting somewhat like a tone control would, and want to look into using a parallel resistance instead (fairly high ohms just to nudge the existing impedance a little higher - gotta look into what values would be best, or whether a series + parallel "L" shaped pairing would be the best way... A parallel resistance should increase the impedance in a uniform, non-frequency-dependent manner, if I remember correctly, and wouldn't mess with the output capacitors either, I think. Gotta ask this over at hydrogenaudio for follow-up.

Thanks for starting me on this research mission!

Terry

 

[tbritton]

I did a little research here: http://www.allaboutcircuits.com/vol_2/chpt_3/4.html and it seems to be saying that a parallel resistance can only diminish the inductance, not add to it. So, then, series is the answer after all.

Terry

 

[IPodPJ]

All that stuff is pretty foreign to me. I'd say buy yourself a portable amp... even the Go-Vibe V5 is inexpensive ($75) and sounds excellent. It will certainly decrease your portability, but if you're looking to avoid all this labor, it's a great fix. I'm sure you are probably doing it because you enjoy it and if that's the case, have lots of fun with it. But if better sound quality is what you're after, certainly amp your iPod.

 

[tbritton]

Quote:

Originally Posted by IPodPJ /img/forum/go_quote.gif All that stuff is pretty foreign to me. I'd say buy yourself a portable amp... even the Go-Vibe V5 is inexpensive ($75) and sounds excellent. It will certainly decrease your portability, but if you're looking to avoid all this labor, it's a great fix. I'm sure you are probably doing it because you enjoy it and if that's the case, have lots of fun with it. But if better sound quality is what you're after, certainly amp your iPod.

Heh... I live for this "deep" stuff! But worry not - I'm certain I will break down and buy me a little Go-Vibe V5 one day soon. That or a Xin Micro V5. But I really use the Nano to be just that - NANO - and unobtrusive as possible for portable use. I have much better listening solutions for at home, and I work at home so they get the lion's share of my listening time. I just wanted to optimize my E4c's sound as it comes straight from the headphone jack and be allowed to use EQ if I wanted to for some tunes without distortion ruining it! (BTW - that EQ problem does not go away from using an external amp, if I've heard correctly. Most people using an external amp do not use any EQ, so for most that is a non-issue. But I like to apply EQ for certain recordings, so EQ distortion would remain an issue for me.)

Terry

 

[IPodPJ]

Quote:

Originally Posted by tbritton /img/forum/go_quote.gif Heh... I live for this "deep" stuff! But worry not - I'm certain I will break down and buy me a little Go-Vibe V5 one day soon. That or a Xin Micro V5. But I really use the Nano to be just that - NANO - and unobtrusive as possible for portable use. I have much better listening solutions for at home, and I work at home so they get the lion's share of my listening time. I just wanted to optimize my E4c's sound as it comes straight from the headphone jack and be allowed to use EQ if I wanted to for some tunes without distortion ruining it! (BTW - that EQ problem does not go away from using an external amp, if I've heard correctly. Most people using an external amp do not use any EQ, so for most that is a non-issue. But I like to apply EQ for certain recordings, so EQ distortion would remain an issue for me.) Terry

Correct, Terry.
Which is why I still keep my library at 83% of normal volume (which was a -2dB adjustment in Audacity for Mac). It has a wealth of other features too, and it's all free.
The amp just gives you a better sound still!! It is a much cleaner signal going to a much cleaner amp. The results with the right IEMs are just mindblowing.

 

[tbritton]

Quote:

Originally Posted by IPodPJ /img/forum/go_quote.gif Correct, Terry. Which is why I still keep my library at 83% of normal volume (which was a -2dB adjustment in Audacity for Mac). It has a wealth of other features too, and it's all free. The amp just gives you a better sound still!! It is a much cleaner signal going to a much cleaner amp. The results with the right IEMs are just mindblowing.

I'm looking forward to hearing my E4c's amped one day soon. By all accounts the amp improves the sound quite noticeably!

Audacity seems like a great program, alright! I'm downloading the newest beta and looking it over. nview is another nice program I was encouraged to consider. I can't afford (or don't want to, anyway) an upgrade of Samplitude 6 to current version. http://www.ntrack.com supports my 24/96 Aardvark sound interface, so it is a major contender and has been around for years. I'll check if Audicity has 24/96 support also.

Terry

 

[tbritton]

Well, talk about bumping a post! Four years have passed! 
 
I've been thinking about Gain-staging and MP3Gain and AACGain again recently. These seem like great solutions for knocking down the input levels pre-EQ (move on if you never use EQ - nothing to see here...) so that you are not over-driving the EQ in the player, and thus that is not also over-driving the inputs to the final amplifier stages.
 
Have any new solutions appeared since this post first was made? Can you do something similar to lossless files now?
 
Terry