bass limiter/compressor batch process help

I’m using Audacity 2.1.2 in Windows 7.

I have a huge number of mp3 files I ripped from my CD collection. I play them all via my android phone and an app called Neutron, thru bluetooth into my car stereo.

I used a utility called mp3gain to more or less normalize the perceived volume of all the mp3s. This worked well, most of the tracks are not too quiet or not way too loud, and the audio quality is excellent. However, I’ve noticed one issue.

The bass levels in the tracks vary enormously, from CD to CD. All the tracks ripped from the same CD have the same bass level, but the tracks play in a random/shuffle list and so I’m constantly having to turn the bass on the car stereo, up or down.

Does Audacity have anything where I could create a batch process to compress and limit, minimum and maximum, a set frequency range? Perhaps 32 to 128?

No, Audacity does not have anything like that built in. To do that automatically would not be simple either. Currently you say that you are using mp3gain, which uses the “Replay Gain” algorithm to even out the track volume - that means that the playback level (“gain”) is automatically adjusted for each track. If you adjust the amount of bass for each track so that all have the same amount of bass, you would also need to normalize the overall volume, otherwise Replay Gain will be pushing the playback volume up and down, and the amount of bass will be pushed up and down with it. And then, even if you get that right so that the bass and overall volume is about the same for all tracks, will you then find that the treble goes up and down for different track? You are almost needing to remaster every track in your collection.

One possible solution would be to use a commercial on-line “auto-mastering” service such as LANDR ( $9 per month for the 320 kbps MP3 service). I’ve not used it myself so I can’t comment on the quality, but there are on-line video reviews available.

Another option if you have a separate bass speaker in your car is to use a hardware compressor between the crossover unit and the bass amp.

A “do-it-yourself” software option would be to find a multi-band compressor plug-in that works with Audacity, learn how to use it (they tend to be a bit complicated) and “remaster” a copy of your music collection.

OK . I hadnt thought of looking for a plug-in. Good idea.

I could cue up every one of these mp3s in my digital audio workstation, view it in a spectrometer display and then push the bass up or down depending upon the track… but with 15000 mp3s, this would be a full time job.

it’s probably easier to just keep turning the car stereo bass knob up and down.

:wink: could be.

If you’re big on bass and have are using a sub in your car, it may be worth looking into using a hardware compressor - you would want one with a slow “release” setting so that it acts as a kind of “automatic volume control” for the sub. It should be between the player and the sub’s amp. If you use an active crossover, it should be between the sub output of the crossover and the sub’s amp.

I dont think there is a sub in the car. I think its just two door speakers, but, it sounds so good I’m beginning to wonder. In any event, I’ve never seen any controls in the car stereo menu for crossover or sub. I’ll keep looking, thats not a bad idea either.

The real issue with having to turn the bass up and down is, I dont want to take my eyes off the road. Even to have to look quickly and find the knob…

OK, not an option then.
We get a broad cross-section of music enthusiasts on this forum, and some have HUGE custom speaker set-ups in their cars - the compressor suggestion would be idea for that type of set-up.

I’d probably just go for setting the bass a little high for the bass heavy stuff, then leave it at that and concentrate on driving :wink:
Mostly it’s not a problem for me because I tend to listen to the radio when driving.

seeing as how the bass heavy stuff rattles the speakers, especially in the right door… (I’m wondering if its already blown or partially blown)

its probably smarter to leave the bass on the low side and only mess with it if it seems non-existent…

thanks for your replies. I think its probably more trouble than its worth to try and work on the mp3s themselves.

Izotope Ozone has a [u]Matching Equalizer[/u] but Ozone costs about $200 USD. I’ve never used Ozone and I don’t know if you could batch process your files. And, I’m not sure if you can confine the EQ-matching to the bass range.

You can find other matching EQs but I have no idea if you can find a free (or cheap) one.

You’d also have the issue of decoding/re-encoding your MP3s. (You have the same issue when you edit/process in Audacity or any “normal” audio editor.)

The sound system in Lori (my lorry) sounds much better than the stock system in pickup trucks. It took me a while to catch on what I had. I have the usual tiny speakers in the dash plus a separate amplifier and huge speakers in the rear side panels. It sounds terrific—but it doesn’t appear in any of the service manuals or brochures.


If your system features a bass doubler or other tricks, then yes, you could have speaker damage. You know the sound system joke: you can hear your friends coming from three blocks away (whom whom whom) and their car appears on the Cal Tech earthquake sensors.

“It’s Koz’s buddies again. Tell them to knock it off.”


G-Multi is a free multi-band compressor plug-in which works in Audacity [on windows].
Although I’m not sure if that type of plug-in will work in Audacity’s batch-processing mode.

VST effect plugins can in principle be added to Chains.


I looked at that, and after messing around with it in my recording program, I decided that theres no real preset that could be created that would work on every file in my archive… because I couldnt really figure out how to establish a minimum/ceiling level. Without that, if I tried to do a few files and guess, I’d probably end up with a whole bunch of files where the bass was now super loud or super quiet.

I dont think theres probably any way to do this in batch, they’d all have to be done one at a time and that would take forever.

Theres also the issue that it might be my phone/music player app, because this is all new for me. Previously I had been listening to music in my car via a small mp3player, and then transmitted into the car stereo via a Coby FM transmitter thing. I never noticed it then, however, the sound quality wasnt anywhere near as good.

So part of this issue might be the phone or the app or the bluetooth connection into the stereo. Probably too complicated to find the real culprit.