I just bought a new pair of headphones and on the box it indicates it works with “Hi-Res Audio”. What the heck is that?
To understand what Hi-Res Audio is, we’re going to have to travel down the proverbial rabbit hole and talk about music, audio, compression and data bandwidth. It’s going to get a bit wooly, but let’s start with a simple executive summary: Most music you listen to on your devices is compressed to make the actual data files smaller and easier to download and work with. Smaller audio files = more songs and CDs on a given storage device, whether it’s your smartphone, iPod or computer.
Further, the same effect applies to streaming services too, because compressed music takes up less bandwidth when it’s compressed than when it’s in all of its original digital glory. Think of water in a pipe for an analogy: If you can get by with less water per unit time then you can have a smaller pipe and end up with a very similar shower or plant watering experience anyway. That’s how your house was designed!
The real issue isn’t the compression, however, but the fact that most all of the compression algorithms used are “lossy”. Lossy means that when the data is compressed and then uncompressed at the point it’s going to be enjoyed, some of the data has gotten lost on the way. Now it’s not like the backup singers vanish or there’s no tuba in the orchestra, but the overall sonic experience is diminished versus the original source.
To look at this digitally, here’s a really great graphic illustration of the data per second of various audio formats:
As you can see, an MP3 audio file has fairly little audio data, a modest 256 kilo-bits per second. Some Mp3 files are even half of that which makes ’em mighty small when it comes to storage requirements, but the audio quality? Maybe good enough for while you’re driving and there’s road noise too.
A music CD is considered a reference source nowadays, but even that’s only about 5x the data of a downloadable song from iTunes, Amazon, or similar, at 1,411 kb/sec. Where you really get into a lot of information that captures all the nuances and subtlety of the original source, however, is with Hi-Res, which at 24 bits is an impressive 4,608 kb/sec.
With that as the background, your headphones include circuitry that lets it reproduce the full range of this Hi-Res music. That’s good. The challenge is to find hi-res audio sources, however. You can change how you rip audio CDs in iTunes (see this page for more information on the options) but a lot of audiophiles either switch to FLAC (free lossless audio codec) format or actually go to a hi-res audio online music store like HD Tracks or iTrax instead.
In general, look for these audio file formats to ensure that you have Hi-Res content: Uncompressed can be PCM, WAV, AIFF and DSD, or FLAC and ALAC support compressed but lossless audio files.
I hope that helps you get started in the world of Hi-Res audio. Figure it out and you’ll be delighted at how amazing your new headphones will sound!
Dave – the reply is a good explanation of the difference in digital data storage/transmission rates. To dig a little further, the human ear hears and interprets changes in air pressures, which is an analog phenomena. That analog phenomena has two main properties, frequency and amplitude. To digitally store and reproduce analog sounds means repeatedly measuring and storing the amplitude. The more frequent the measurements, the higher the frequencies that can be reproduced. The more bits per measurement, the better the resolution of the air pressure changes.
Teen agers who haven’t spent much time at rock concerts, or under cranked up headphones, can hear sounds up to around 15,000 hz. To digitally reproduce this requires amplitude data to be measured and recorded at a 30,000 hz rate. Claims to distinguish sound much above this frequency are more like the emperor’s new clothes – a claim to see or hear something that really isn’t there.
Things get a lot more complicated when measuring the amplitude of sound pressure. The ear perceives sound amplitude in a logarithmic manner rather than a linear manner. And different frequencies are perceived differently. The teen age ear can clearly distinguish relative changes of “sound” or air pressure of over 120 dB at some frequencies. Unfortunately, 24-bit resolution by itself won’t give 120 dB of resolution, only about 80 dB. Most recording equipment processes and stores the amplitude signal as a quasi-logarithmic value – so there is some ‘loss’ of raw data in the process.
Now the math – 30,000 hz of 24bit samples is only 720 kbps, or 1,440 kbps for 2 channel stereo. (See the graphic above for the data rate attributed to a music CD.) Unless you are a teen ager who can actually find recordings with 40 bit amplitude, consider spending your money on additional standard CD quality recordings from talented artists, rather than on Hi-Res audio equipment.
As a side note – top notch spoken voice recording requires only about 48 kbps per channel. That is because (1) virtually all spoken audio nuance can be heard at 3000 hz and below, and (2) 7 bit amplitude, logarithmically encoded, is enough.