Bit rate question

Edited: August 3, 2017, 9:04 AM · I wish to get the most compression of recorded music practical on the 256 GB iPod I expect to obtain soon. I would like to sync my entire 415GB iTunes library to the iPod and have room for additional downloads. I am using 192kbps mp3 compression in my iTunes library and 128kbps in my current 160GB iPod Classic. (I previously used 320 kbps in iTunes but then decided I needed more "room" and did a "do-over" of the entire library. It still works the same for my poor ears)

My hearing is poor and even with digital hearing aids it is down 60 db at 5KHz. The speakers I use with my iPod (via bluetooth) are not great, I use the iPod & speakers for background music in a store where I work part time. When I want to listen to music at home I have several other options and I would not use my iPod "on the go" other than to plug it into the car radio-something I only tried once in 8 years of iPod ownership.

So I wonder if I can get away with 64 kbps compression for my purposes. What will I lose within my hearing capability?

Replies (17)

August 3, 2017, 8:56 AM · If you listen to a lot of violin music, it will sound very "glassy" at low bitrates. I wouldn't recommend it.
August 3, 2017, 8:57 AM · What is "glassy?"
August 3, 2017, 9:06 AM · Thin sounding.
128 is what you could aim for in your case. For HiFi I use flac only, but on my mobile 192 is fine while 128 is ok. Less is even bad to hear with the smartphone.
August 3, 2017, 9:09 AM · Its probably a subjective term.

A larger compression means that you get a lower bandwidth. If you compress too much, you end up losing the high and low part of the spectrum (very high and very low notes).

If your earphones have bad bass and do not respond well at high pitches (if your earphones are cheap enough), you will not notice the difference at all.

August 3, 2017, 10:14 AM · With a 256 GB Ipod you will be able to put hundreds of CDs on it using Apple Lossless Compression (I use FLAC on my non-apple devices). I can hear the difference between 320Kb/s and lossless, and you probably can too. Lossless is the way to go.
August 3, 2017, 10:24 AM · At high compression rates, I find that a violin starts to have a sort of sharp, hollow edge to the sound, as if the string were glass that were being scraped. That's what I meant.
Edited: August 3, 2017, 11:46 AM · Thank you all for your inputs. I don't know what is clipped when mp3 files are compressed. With too much compression I might miss very crisp transients - I don't know, but because of my hearing deficit I am unable to appreciate musical sounds above about 3,000 Hz and I really resent the dynamic range available on CDs because if I can hear orchestral pp or ppp, I cannot tolerate ff - and my wife definitely can't..

My purpose in describing the poor state of my hearing, etc., was to try to learn how low I might go in bitrate compression without noticing it. I already have thousands of CDs in my iTunes (40,500 tracks) and about half that many in my 160GB iPod.

August 3, 2017, 2:59 PM · Try it and decide for yourself. I would suspect you will hear some type of degredation
August 4, 2017, 1:17 AM · Jason, mp3 fixed bit rate compression is far more intelligent than just making a smaller frequency range. Its not just in high and low frequencys different when you choose a lower bitrate. That would be digital stone age.
August 4, 2017, 7:29 AM · For mp3, 128kbps is the rate at which people typically begin to notice a difference between the compressed and uncompressed stream. Smaller stream rates will work for normal speech.

Apple has its own compression called AAC. I am not sure if it gives more compression with less loss.

There are "lossless" audio compression standards, like FLAC, that will play on many players that accept mp3.

Not a direct answer to your question but it gives you a few other things to research before making a decision.

August 4, 2017, 12:26 PM · Aac is about the same in terms of result, slightly more options but basically the same idea. In the usual rates you wont be able to call one better or worse. Is it really closed apple stuff? I thought they just jumped on it and helped coding, but I didnt do research on that.
The main problem I see here is: resampling mp3 will cause a lot of quality loss. You should always sample from a lossless file.
August 4, 2017, 1:09 PM · Newer compression formats like Ogg Vorbis and AAC will sound comparatively better than MP3 at the same bitrate. I don't recommend compressing anything below 128 kbps j-stereo though. Especially for classical music, the compression artifacts stick out horribly.

Edited: August 4, 2017, 7:25 PM · Cancel the order and buy FiiO X7 or X5.
FLAC (lossless compression) format rules! I too have a hearing deficit and was astonished how much better FLAC is than any of Apple's bad apples.
August 4, 2017, 6:50 PM · @ Rocky I agree, FLAC is one of the best types of compression to use if you must compress. 256-320 mp3 is passable 128 is not very good. 64 mp3 is horrible no matter what the program material is.

iTunes decided to have songs in their library labeled with a "mastered for iTunes" as 320 AAC files. In order to get that designation the album must be mastered by one of their qualifying studios.

The standard online streaming resolution from most vendors is 128 mp3. In order for compression to work the algorithm tries to determine everything your ears won't hear and then deletes that material. I have a plugin that can let me hear the artifacts left over after compression to 128 mp3. These artifacts are in the music as a result of the compression. In short, it's a horrible sound at 128. At 256-320 not nearly as bad.

The really sad thing is I export a 48/24 master and it gets uploaded to Soundcloud and compressed to a 128 mp3. This is like taking a Picasso and scanning it to print in a low resolution. It's amazing how much detail the average listener doesn't realize they miss as the result of compression.

Using the Apple cloud might be something to consider.No matter what I wouldn't compress to 64, and if I had my files in 320 already I wouldn't even go to 128. Maybe get a larger ipod? Transfer some files to a computer. It doesn't need to be a mac since iTunes is cross platform.

Edited: August 5, 2017, 7:55 AM · I went through this exercise some years ago when my ears were better than they are now. I recorded a few minutes of symphonic, chamber and solo violin music from good quality CDs as wav files at 44kHz sampling rate, and saved them successively as 320, 256, 224, 192, 160, 128 mp3 (I didn't have FLAC). Then I spent an hour listening to and comparing the recordings. I couldn't tell the difference between 320 and 256; 256 v 224 was just about discernible with very careful listening, but certainly not off-putting; 192 was starting to get noticeable, and 160 more so, but both were perhaps bearable for some kinds of music or music from radio; as for 128 - forget it except for spoken voice on radio.

Another thing that you could do if you want to use a bit of geekery is to digitally subtract the mp3 file from the original wav file and see on the screen what has been lost in the conversion.

More recently I've experimented with FLAC and am not at all sure I can tell the difference between that and 256/224, so I use FLAC now for backing up CDs or LPs - the size reduction is usually about 40-50%. My mp3s for music listening are all 256 or 224.

A point that I think is worth making about all this is that if you're not careful you could find yourself listening to audio quality rather than the music itself, and that should not be the obect of the exercise. A follow-on point is that the brain is perfectly capable of ignoring all sorts of unwanted noise when you're really listening to the actual music.


August 5, 2017, 9:13 AM · Well, Trevor, it depends a lot on at least 3 factors:
1. recording technique and sound editing (you will not notice the difference if recording is poor)
2. quality of audio equipment used in reproduction (cd player, amplifier, speakers) - you will not notice the difference if reproduction can not support high quality of recording
3. room - your room can distort sound up to the point that nuances are not noticeable

It also depends on our ears and how well are we trained or habituated in sound perception. It is very easy to get conditioned to poor MP3 quality and budget-class player, etc....

I have compared iPod (mp3, m4a) and FiiO X5 1st generation (FLAC) using Bose QC 25 headphones. The difference is apparent in sound clarity, dynamism (ppp to fff), range, colour, etc.
It also has more of the "immediacy" of the sound, especially with solo recording and chamber music up to octet.

August 5, 2017, 9:49 AM · Rocky, I should have mentioned that I used, and still use, Sennheiser HD205 headphones - perhaps not Bose quality, but certainly not bad.



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