One way to get around EQ distortion on the iPod

Update: Recently a solution for users of the AAC format has become available, please scroll to the end of the article for more information.




First, lets start off with some background information on the iPod's sound quality. The Apple iPod is a very balanced player sonically. It is renowned for its clear, detailed sound and it doesn't provide emphasis on any particular frequency in its sound range. While this is beneficial, as it doesn't add any artifacts to the original recording, the iPod's sound has been described as 'flat' and uninvolving by some consumers due to this fact. Conversely, many of its competitors employ special processing - such as boosting bass response - in order to create a more 'fun' sonic character generally liked by these consumers. Therefore, in comparison, the iPod is seemingly lacking in bass.

It has also been discovered that when used in conjunction with certain headphones, there is an actual deficiency in the lower frequency response. A German magazine, Stereoplay, has published the following graph, showing poor bass response when using headphones with around 25 ohms of impedance.



Marc Heijligers states on his website he has further tested the iPod and concludes that there is a similar roll-off in bass for headphones ranging from 16 to 32 ohms. This is somewhat worrying, as most consumer headphones fit within this criteria - including the earphones bundled with the iPod itself. Personally, however, during testing with Sennheiser HD 497 headphones (which have an impedance of 32 ohms), I found the bass to be sufficiently present. It was not as strong as my Panasonic SL-CT500 MP3/CD player, but this is understandable as the Panasonic uses processing to artificially boost bass, as I have stated above. I do not have scientific proof of this, but I have come to this conclusion after comparing several sources.

In my opinion, the iPod's bass response is fine, its just that some people prefer a more dominant bass, as provided by players such as the iRiver H-Series, or my Panasonic CD player. While I can appreciate the accuracy quality of the iPod's sound, there are times when I too feel that some extra bass wouldn't hurt. This is entirely dependant on user preference, and even mood, so perhaps in acknowledgement of this, Apple has included several equalizer presets on the iPod. Many audio players have this feature, and some, such as the Rio Karma offer a parametric equalizer that can be used to tweak sound with great control over specific frequencies. An equalizer enables you to change the sound output of your player to suit your sonic preferences - for example, boosting or reducing bass or treble, in the simplest form of equalization. Unfortunately, however, unlike the Karma, the iPod's equalizer is horrible. Many users have found it distorts the sound far too easily, even on undemanding songs. This is a shame, as some of the iPod's equalizer presents can emulate the 'fun' character of other players and satisfy a wider range of users. In its current state, it is quite unusable.



Many users have given up on the equalizer presets on the iPod. The "Bass Booster" preset did not have much impact, for example, as on bassy hits in music it simply caused crackling/distortion. When I first received my iPod, I was quite pleased with its sound. On some genres of music, especially music reliant on bass, however, I wished for a little more fullness in the lower frequencies. This is when I began to research on the internet about solutions to the equalizer distortion problem on the iPod. If somehow I could manage to eliminate the distortion, the iPod would have much more versatile sound - one that could be tweaked for the situation.

Perhaps the easiest way to overcome the equalizer's shortcomings is to just not use it! Bangraman at the Head-Fi forums recommends headphones such as the Sennheiser HD 25-1, the Beyerdynamic DT231 and the Sony MDR-G74SL for use in conjunction with the iPod. These headphones apparently emphasize bass, which in turn acts as a de-facto equalizer. I say "apparently" as I have not tried any of these phones. I would recommend you test-drive these headphones however as they may be exactly what you are looking for. I have tried some low-end Sennheiser headphones which had overemphasized bass, and I can, in that respect, testify that a headphone can make a huge difference in your iPod's sound signature. I would also like to add the Koss KSC-35 to that list, as it is often touted as having strong bass.

Headphones, however, cost money, and factors such as portability also need to be considered. Also, you can't turn off the colorations in your headphones, so you are stuck with that particular sound. Headphones cannot be tweaked for the situation! This is not the ideal solution for everyone, and most people would prefer it if the equalizer just worked. I'm sure that you'll be pleased to find out that with a combination of iPod tweaks, equalizer distortion can be fully eliminated. I am now listening to my iPod on the "Bass Booster" equalizer preset. I am hearing no distortion, and the iPod outputs bass that can rival my CD player in loudness.

Let me guide you though the steps I took to eliminate my iPod's equalizer distortion. Firstly, I used a freeware, open-source program called MP3Gain to reduce the volume of my mp3's. Don't worry; MP3Gain does not affect your mp3's at all! Every mp3 file has a tag within it which determines the loudness at which it is played. The iPod's (or any other) mp3 decoder reads this tag when it opens an mp3 and outputs the music stored within the file at a level that corresponds with this value. All MP3Gain does, is change this value to a lower level - it does not change anything else within your files. The audio quality is not affected in the least bit - I can attest to this personally, as I have MP3Gained around 2000 mp3's (on my iPod). Moreover, all of the changes MP3Gain does are completely reversible.



All mp3 files have a default volume tag of around 95 to 105dB (decibels - a unit of loudness). When the iPod plays at this output volume, distortion does not occur. When you boost the iPod's bass however, with the equalizer, you are increasing the volume of the lower frequencies past this value (in order to make them more prominent amongst the other frequencies of the sound), and this, in turn, causes clipping and distortion. Basically, the iPod's amp is trying to output a volume that is greater than its inbuilt volume limit - so it serves crackling. By using MP3Gain to reduce the volume tag of your mp3 files to around 89dB, we can leave some headroom to further boost some frequencies without overdriving the iPod's amplifier.

For example: if you boost the 60Hz frequency (low bass) by around 10dB, the iPod will output that frequency at 99dB (89 + 10). At 99dB, distortion does not occur. If you boost a song playing at 105dB by 10dB, however, we get a total of 115dB which, no doubt, has passed the threshold of distortion. From experience, 105dB is about the limit; we need to reduce the volume tag value of our mp3's significantly below 105dB to avoid distortion. 89dB is the value recommended by MP3Gain developers, and I concur, as this value has eliminated all distortion on my iPod that used to result from boosting frequencies via equalizer presets.

A note about decibel values: these are the values stored within the mp3 file itself. The actual, real-world, loudness of the file will depend on the strength of the iPod's amplifier (which outputs 30mW of power at a load of 16 ohms), and headphone sensitivity (in other words: decibels per milliwatt (mW) of power). Take the dB figures in this article as synthetic.

At the MP3Gain website, click "Download" in the navigational bar at the top. Once you are at the download page, select the latest version of MP3Gain. It should download and install very quickly. To MP3Gain your files, use the "Add File(s)" or "Add Folder" buttons to tell the program where your songs are.



Make sure that the "Target" volume value is 89.0dB and hit "Track Gain." MP3Gain now has to analyze each mp3 that you selected and apply the new volume information. Depending on the number of songs, this can take several hours. It took me around 9 hours to process around 2000 songs in less than ideal conditions: my mp3's were on an external hard drive using a USB 1.1 connection - which is slow. Processing another 2000 songs on my primary hard drive, the time was halved. Either way, its best to start it in the morning and leave it while you are at work/school. The hassle of going through this is worth it as you end up with usable equalizer presets on your iPod.

Once this process has finished load the mp3s onto your iPod. If you want to skip this step, it is possible to point MP3Gain to the "iPod_control" folder, located on your iPod. This way, the actual files on your iPod will be processed. I have tested this, and it works just fine - but I wouldn't recommend it as running your iPod's hard drive for several hours and without any sort of cooling might be damaging. My iPod quickly heated up and I had to abort the process at around 10 or so percent.

You are now almost done. Play a bassy, freshly MP3Gained song and go straight for the "Bass Boost" preset. An mp3 with a volume value of 89dB should not distort at all! You can go through all of the presets to find one that you find a liking to. I've listened to around 50 or so of my songs so far, and as of yet not one has distorted.

We could just leave it there, but as you probably have noticed, the output volume of the iPod has softened. After MP3Gain, I used the iPod, volume set at around 95% (up from about 75%) - to compensate for the lowered mp3 volume value. You shouldn't be discouraged by this. Like me, you probably want a little more power on tap - and there is a solution to this also. Espen Ringom has developed a tool called euPod, to raise the volume of european capped-volume iPods - due to a French law limiting the output power of portable devices - to the same level as United States or international iPods. The good news is that it can also increase the volume of US-spec iPods by up to 80%, cleanly and without distortion. The use of euPod, again, is completely safe: it does not make any permanent changes. It works by changing the volume information of your files, similar to MP3Gain, but not in the actual mp3's, in the iTunes music library file. This file is located in the "iPod_control" folder on your iPod. I do not know the exact specifics, but I can confirm that it does result in your iPod playing more loudly, and that it does not cause distortion. The use of euPod can balance the decrease in volume that occurs as a result of the use of MP3Gain.



Simply move the slider to your desired value and press "Boost iPod Volume." I have found that a 10 to 20% boost completely compensates for MP3Gain. You can if course gain even more volume if you so desire. Some people have stated that the iPod's sound goes "off" or becomes unbalanced past 40%, but as you can always turn it down or turn it off, feel free to experiment for a setting which suits you. I have gone up to 80%, but this is overkill as you'd never turn up the volume past half way on the iPod - I see no point. It nevertheless is safe.



One positive aspect of using MP3Gain is that all of your songs will be equalized. This will account for volume variances between albums so you wont have to adjust the volume as frequently. MP3Gain uses the established ReplayGain algorithm to determine how loud we perceive a track to be (not how loud it actually is) and then it normalizes it to align with the rest of your songs.

The iPodlounge forums and the Head-Fi forums have been useful in gathering information about this issue. iPodlounge is obviously a site all about the iPod and Head-Fi is a forum where audio enthusiasts discuss portable audio, headphones and other audio-related topics. Both sites have a wealth of information.

I hope that this information improves your iPod experience.


After further listening, I have found the "Bass Boost" preset, while clean, to be very 'dark' for a lack of a better word. Its a little too much for my likes. I have found both "Latin" and "Rock" to be quite enjoyable as they dont emphasise the bass as much and also add some treble for than fun "V" sound. Overall, the Acoustic preset is the most enjoyable for me - just the right amount of bass. These presets are great on the go - for example on the bus - as the extra bass balances out the noise from the engine and other passangers.


Up until recently, the method described above applied only to MP3 users. The MP3Gain website's front page has information on AACGain. This may be of use for those who use AAC files. The MP3Gain developers have used AACGain without probems, but state that it is still in the experimental phase. I have not used AACGain - mostly due to the fact that I dont use AAC files - so I cannot quarantee results. Still try it out on a few files, it may be exactly what you are looking for.


I have done all of the steps detailed in this article on my own iPod successfully and without any damage to my iPod, headphones or computer. The results I have shared here are truthful to my experience but, due to factors outside my control, I cannot guarantee the same results for everyone. Similarly, neither DAPReview nor I can be held responsible for any damage to your equipment arising from taking the actions I advise in this article. Again, this has worked successfully for me, but try it at your own risk.