Posts

How It Works: Audio Compression

The term “compression” is often a source of confusion when discussing digital music. There are two kinds of compression. The first is the kind used to compress the size of files; this is data compression. There is lossy compression, using with MP3 and AAC files, and lossless compression, used with FLAC and Apple Lossless formats.

But the other kind of compression, dynamic range compression, is the much derided method of limiting the amount of dynamic range in music. The point of dynamic range compression is to make less of a difference between the quietest parts of a piece of music and the loudest parts. Most music is compressed as part of the recording and mastering process, because it does sound a lot better, and keeps you from blowing out your speakers. But over-compressing music makes it sound like crap.

The best way to understand dynamic compression is to look at a couple of audio waveforms. The screenshots below were made using Rogue Amoeba’s Fission audio editor.

Here’s a song which is free on iTunes today. I chose this one because, well, any free pop single is likely to be heavily compressed, and this example shows that I’m not wrong.

001.png

You can see two things in this waveform. The first is that the song is almost universally loud; the waves show the loudness. The second thing to notice is that there is a lot of clipping; audio volume that hits the top of the available limit. This is bad. As Wikipedia says:

Music which is clipped experiences amplitude compression, whereby all notes begin to sound equally loud because loud notes are being clipped to the same output level as softer notes.

Excessive compression has led to what is known as the loudness wars. This is when record producers make their songs louder and louder so they stand out against other songs. Generally, the human brain perceives louder music to be better, so additional loudness can make a song more compelling. But, in the end, all this has done is made lots of loud, clipped songs.

Here’s an example of a song which is not compressed. This is Pink Floyd’s Wish You Were Here:

002.png

You can see the difference in two places in this screenshot. In the overall timeline at the top of the window, you can see that the music has a shape; in the first screenshot of the free pop single, it’s just one long mass of sound. And in the actual waveform, you can see that there is modulation, and no clipping, in the Pink Floyd song.

The difference is that you may play your Pink Floyd song at a louder volume, in order to hear the quiet parts of the song, but the louder parts will be, well, loud. In the first song, the entire song is loud, and you’re likely to become fatigued more quickly after listening to music like that.

For good examples of audio that is not compressed – or only very slightly – watch a movie. In general, movie audio is not compressed; this is why the dialog is often too soft, but the special effects are too loud. This is why you often need to adjust the volume for movies with lots of explosions, otherwise your ears hurt. (You may have an AV receiver which has a dynamic range compression feature; if you’ve turned this on, you may not hear such large differences in volume.)

Dynamic range compression isn’t a bad thing; it’s just bad when it’s overdone, as is the case in much popular music today.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

My New Mono Listening Setup

If you follow this blog, you’ve probably noticed that I have a thing about mono recordings. I wrote about my recent appreciation for these recordings in In Praise of Mono Recordings, and offered a list of Some Great Mono Recordings.

The problem with listening to mono recordings in stereo – on two speakers – is that there is a sweet spot, the point where the sound converges, just as there is with stereo listening. With mono, this sounds artificial. In addition, it’s possible that there are phase cancellation problems when you listen to the same music coming from two speakers.

I did a fair amount of research, and found that there is a small minority of people – audiophiles; I know… – who have dedicated mono systems. I didn’t want to go that far; I could buy a mono amp, but I see nothing wrong with using just one channel of a mono stream connected to a single speaker to listen to mono recordings.

So I decided to get a mono listening setup for my office. You can see, in the photo below, my new speaker on a stand behind my monitor; it’s a bit tilted; I need to work on that.

2014-04-09 11.12.29.jpg

My amp – a Cambridge Audio 651A (Amazon.com, Amazon UK) – and it has two speaker zones. So my stereo speakers are set on zone A, and I connected a single speaker to zone B.

My current speakers in my office are Focal Chorus 705v (Amazon.com, Amazon UK). I also have a pair of Focal Chorus 806v speakers (Amazon.com, Amazon UK) in my living room. I bought the latter about a year and a half ago in France, and I really like their neutrality. So when I was looking for new speakers for my office, I went with the same brand, just smaller.

So, when looking for a mono speaker, I checked out what Focal has to offer. I realized that the best thing might be a central speaker from a surround system, and I got a Focal Chorus CC 700 (Amazon.com, Amazon UK). It has two mid-bass drivers and one tweeter, and has a wonderfully balanced sound. The mid-bass drivers are slightly larger than those on the stereo speakers in my office; this center speaker is more adapted to a system using the 806s. But since I’m only using the CC 700 on its own, and not as part of a multi-speaker system, it doesn’t matter. (If there had been a smaller version of this speaker, I would have gotten it.)

Focal-Chorus-CC-700-Noyer_P_1200.jpg

This setup is certainly not a necessity, but I like the idea of listening to mono music on a single speaker. It wasn’t too expensive – I got it much cheaper than Amazon’s price – and it’s got nice, clean sound. Mono music sounds a lot better like this.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

Do Vinyl Records Sound Better than CDs? (Spoiler: Nope)

I’ve been discussing a number of audiophile myths here on Kirkville, and today I’d like to address another one: the myth that vinyl sounds better than CDs (or downloads). Vinyl sales are booming, reaching the highest levels in more than ten years. To be fair, this isn’t difficult; as long as sales continue to increase, they’ll be higher than any time since the Great Vinyl Decline of the late 1980s and early 1990s.

People abandoned vinyl for several reasons: CDs were more convenient, less fragile, and sounded better[1]. Turntables were annoying and fragile, and you had to manually change sides of records; with CDs, you can play an entire album without flipping discs.

I grew up with vinyl, and, while I miss the bigger artwork, and the added room for liner notes, that’s all I miss. I don’t miss the clicks and pops of vinyl, or the way that, if you bumped into the turntable, or whatever shelf it was on, you could scratch a record, damaging it permanently. With older, scratched records, sometimes the only way to listen to them was to place a penny on the cartridge to add weight to it. Also, the quality of the plastic used for vinyl records was often poor, meaning that records wore out quickly. Oh, and you had to deal with dust, records that warped if exposed to heat or were stored flat, static electricity that could perturb things, the spindle hole that might be off-center, and wow and flutter that added noise to playback.

But the biggest problem with vinyl is simply that records wear out. Audiophiles tout the higher frequency response of vinyl over CDs, saying that vinyl can play back those frequencies that we can’t hear.[2] First, this is only true with a pristine record, a perfect stylus, and a high-end stereo system; in most cases, vinyl’s frequency range is lower than that of CDs. Bear in mind that needles used to play records are made of diamonds, a very hard substance, and each play of a record wears it out a bit. This wear results in lower frequency response and lower overall fidelity. Stereo separation is poor on vinyl; there is spillover from one channel to the other, which is an inherent weakness of the playback process. And, because of RIAA equalization[3], the sound on a recording is manipulated, both for pressing, to reduce low frequencies, and for playback, to attempt to restore them.

But there’s another problem with vinyl that most people don’t consider. The first grooves on an LP offer 510 mm of vinyl per second, but as you get to the end of a side, there’s only around 200 mm per second; less than half the resolution. This is similar to the difference in tape speeds dropping from, say, 15 ips (inches per second) to 7.5 ips. Anyone who has worked with tapes knows that this speed difference results in much lower fidelity. Back in the LP days, musicians would argue about who got their songs on the beginnings of sides, and the music you listen to on an LP gets lower in quality as you get closer to the center.

Most people, when discussing vinyl, talk about an “analog sound,” saying that vinyl sounds “warmer” or “richer” than digital. It does; because there is less frequency response (poorer reproduction of high frequencies), and more distortion. Just as tube amps may sound “better” because of the distortion they introduce into playback, the same is true for vinyl. That “warmth” you hear is simply the poor quality of the playback; the distortion caused by the analog chain, and its lack of detail.

“But the other part of it is that the experience of listening to an LP involves a lot more than remastering and sound sources. There’s the act of putting a record on, there is the comforting surface noise, there is the fact that LPs are beautiful objects and CDs have always looked like plastic office supplies. So enjoying what an LP has to offer is in no way contingent on convincing yourself that they necessarily sound better than CDs.”[4]

There’s a fetishism around vinyl, it’s about the process of listening. If you take more time to prepare for something, it’s likely that you’ll enjoy it more. If this is what you want, then by all means, go for it; but the sound of vinyl is actually inferior to that of CDs or digital audio.

So this is yet another myth that’s used to market products to people who don’t know better. You may like the idea of vinyl, but my guess is that, if you grew up with vinyl, you are probably aware of its limitations, and don’t want to go back into the past. I find it interesting that many audiophiles prefer a format that provides audio in a lower quality, and with more distortion.


Let me close with a few tidbits from turntable reviews in hi-fi magazines.

Each instrument and voice sat unambiguously in the soundstage with a largeness and roundness at its edges—the opposite of an analytic and etched sound.

Kraftwerk’s The Man-Machine sounded brilliant on the Clearaudio Ovation, which lent just enough warmth and body to the sound to humanize this music while not obscuring its drive and pulse, its stops and starts.

the music was a steady stream of sound that quickly became a river, then just a few drops

produced a big, slightly warm orchestral sound. String tone was rich, with a pleasing golden glow. The piano’s lower register was cleanly rendered and remained well defined against the hall’s reverberant field. The upper keyboard sounded supple, with a rich, woody, yet sparkling bite. Image stability and solidity were never in question, and the system’s dynamic punch announced a turntable that seemed in complete control.

And, I’ll finish with another gem from What Hi-Fi?:

Play an album such as Nirvana’s Nevermind and the Point 5 delivers an energetic sound that combines fluidity, stability and authority brilliantly.

Where most rivals render a sharply etched sound packed with detail, the Point 5 has a more rounded presentation where the leading and trailing edges of notes aren’t overly emphasised, but the bits in between are defined richly.

The result is an immensely likeable presentation that’s big and muscular without suffering from a lack of agility or finesse.


  1. Yes, many early CDs sounded bad, because mastering engineers initially used masters created for LPs, and it took a while for them to, well, master the process for the digital medium.  ↩

  2. See Music, not Sound: Why High-Resolution Music Is a Marketing Ploy.  ↩

  3. https://en.wikipedia.org/wiki/RIAA_equalization  ↩

  4. Pitchfork: Does Vinyl Really Sound Better?  ↩

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

How Hi-Fi Magazines Write about Cables, Part 9

61-GbTPO+oL._SL1500_.jpgI hate connecting speaker wire to speakers and amps. I finally broke down and bought some banana plugs: I bought 24 of them. (Amazon.com, Amazon UK)

With banana plugs, you run your speaker wire in the big hole in the side, after unscrewing the bottom part, then screw it shut to hold the wire firmly. You can then insert the plugs into the speaker terminals, assuming your speakers are compatible with banana plugs.

As you can see, the banana plugs I bought aren’t expensive, but you can spend a few hundred dollars on a pair of them. Remember, for a stereo with two speakers, you need four pairs: one for each end of each speaker cable.

So, I naturally went in search of reviews of these audiophile banana plugs. I was surprised that I didn’t find any. Imagine spending a couple thousand dollars on speaker cables, then putting $2 banana plugs on them. Wouldn’t that ruin the entire system? Apparently not; even in audiophile forums, I don’t see any kind of raving about top-of-the-line banana plugs. (Many expensive audio cables come with banana plugs fitted, but not all.)

So, if the cable is great, it makes a difference. But you may connect an expensive cable to your speakers or amps with cheap banana plugs, and that has no effect? Interesting.

If anyone does find reviews of banana plugs, let me know.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

How Hi-Fi Magazines Write about Cables, Part 8

There’s a phenomenon that audiophiles know well: burn-in, or break-in. Every single audio component you get, according to them, needs to be burned in. You need to run it for days, even weeks to get optimal sound. This is necessary for speakers, amps, CD players, and, yes, cables.

The concept of burning or breaking in physical devices, such as speakers, makes sense; speakers turn electrical impulses into music through vibrations, and it’s logical that a speaker, and its housing, will react to those vibrations. But suggesting that cables need to be broken in; well, that’s just typical audiophile BS.

Here’s a review of a set of cables; the reviewer has an interesting approach:

I will only review a complete cable loom, regardless of which manufacturer is supplying it. This should comprise of everything from the mains leads, through the interconnects to the speakers and might also incorporate data cables if a computer is included in the system.

Of course, this doesn’t make his review any more grounded than others. Regarding burn-in, he says:

After about three weeks of daily use the cables began to undergo a change. There was always a slight question mark in my head over their absolute resolving power through the midband and after initially feeling very complimentary of their impeccable balance they seemed to grow a little soft and somewhat dull. But, gradually a new performance level was taking shape and they just grew in sophistication and balance as the weeks rolled by. What emerged was an even livelier cable set than before with an extra edge and clarity to their dynamic resolving power. The system had put on some weight, but in all the right places, drawing the electronics together as a more enjoyable whole with an even better feeling of stability to the musical picture. Now the system was sounding like a single musically focussed unit rather than a collection of expensive components.

But then he changed one cable, the interconnect between the CD player and amp:

I am not saying the system sounded bad. In fact the sound became warmer and fatter, but the rhythmic togetherness and the whole swing and beating pulse of the music had vanished. Now it stuttered along like so many high-end systems I hear. It was certainly impressive hi-fi, but the detailed focus and explicit telling of the musical story was severely compromised.

Ah, the explicit telling of the musical story… It’s a shame when it’s severely compromised.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

How Apple’s AirPlay Streams Audio

I got a question from a reader asking how Apple’s AirPlay streams audio. The question specifically asked about how audio files are converted, and whether AirPlay reduces their quality.

Apple doesn’t provide much information about AirPlay, and I found a number of articles and forum posts where people described complex testing routines to determine the bit depth and sample rate of music streamed to AirPlay devices, such as an Apple TV or AirPort Express. But you don’t need to go to such great lengths to figure this out. Simply open Audio-MIDI Setup on a Mac, and select AirPlay.

009.png

As you can see above, AirPlay streams at 16-bit, 44,100 kHz. However, what you don’t see is that AirPlay streams music in Apple Lossless format. What this means is that no matter what format your music is in, it gets converted by OS X – not by iTunes – to Apple Lossless, to ensure the highest quality. So lossless files will be streamed as lossless, as will AAC or MP3 files.

However, high-resolution files will be downsampled to 16/44.1. Interestingly, the Apple TV outputs audio in 48 kHZ, most likely because this is 48 kHz is the standard for movie and TV audio[1]. Movies sold by the iTunes Store contain audio at 48 kHz, but only at 160 kbps.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

When All Our Audio Equipment Is Wireless, Will Cable Manufacturers Go Out of Business?

In a comment to my article Do Cables Make a Difference to Audio Playback?, one of my readers said, half-jokingly:

What will all the audiophiles do when everything goes wireless? Will they be selling us oxygen-free air for a purer transmission?

He has a point. We’re already streaming music, via AirPlay or Bluetooth, to high-end devices. We’re cutting out the cables from a source to either an amplifier or a playback device. And I haven’t heard anyone complain that it makes a difference.

Could it be that it doesn’t make a difference? Or will audiophiles come up with gadgets to improve audio streaming. Not so much oxygen-free air, but gizmos that sit in our living rooms to somehow improve the waves?

What is interesting is that, inevitably, many cable manufacturers will suffer. I doubt they’ll all go out of business; we’ll still be using cables to connect some devices, though I can imagine a day when we won’t need to. And then, I predict, we’ll see audiophiles arguing that using cables is better than using wireless connections. Because, you know, jitter and the like. Impurities in the air. Vibrations that affect the wireless transmission.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone

How Hi-Fi Magazines Write about Cables, Part 7

Just in case you thought What Hi-Fi? was the only magazine out there spewing out reviews about magical hi-fi equipment and accessories, here’s another one I found on the Stereophile web site. I have a feeling that the shelf is going to become the next cable; an audiophile device that contains pixie powder and makes everything sound better.

Here’s a review of a shelf. You don’t need to read the whole thing, but the last paragraph I quote may be the best I’ve read so far:

The Pagode Master Reference HD07 rack really did work—at least with components that had an onboard power supply. Each such component I tried, from the lightest line stage to massive, two-chassis CD players, sounded better sitting on the FE rack than on my Bright Star or Merrill stand. Their focus, resolution, and dynamic precision were all slightly but consistently improved; my listening comments were peppered with such phrases as “faster, cleaner dynamics” and “sharper, more dimensional images.”

Alain Lombard and the Paris Opéra-Comique’s recording of Delibes’ Lakmé was a good example. As I moved each component in turn onto the HD07 rack [...] the image of soprano Mady Mesplé became clearer and more solid. Her vocal nuances were more apparent, and I was able to better hear the trailing edges of her phrases. The rear and sides of the soundstage opened up a bit as well, and the space surrounding the performers seemed more transparent.

Repeating the exercise with two different digital systems and Dire Straits’ “Private Investigations,” from Love Over Gold, produced a similar result, but what I really noticed was the improvement in detail resolution. As each component moved onto the HD07, a bit more low-level detail emerged from the background. Distinguishing the multiple echoes around the scuffing shoes traversing the stage was one great example; another was the emerging presence of several different, distinct effects around Mark Knopfler’s speaking voice.

But it gets better. The reviewer added special feet under the shelf.

On the other hand, installing a set of Ceraball or Cerapuc feet under a component was a huge, jaw-dropping change. The differences were the same—improved focus, transparency, resolution, and dynamic precision—but their magnitude was much larger. Slipping a trio of Ceraballs under the VTL TL-7.5 wasn’t like demagnetizing a cartridge; it was like upgrading to a really good moving-coil. And dressing cables? Forget it—this improvement was like replacing all of my freebie and Home Depot wire with a good set of high-end cables.

There he goes, talking about cables…

But I’ve saved the best for last:

Like a kid in a candy store, I kept adding more and more Cera feet. The effects were similar with each step, and similarly dramatic. The biggest improvements came when I slipped Cerapucs under my VTL Ichiban power amplifiers and between my turntable stand’s steel frame and marble top plate. The soundstage became significantly cleaner and the picture snapped into focus. Images inflated from two dimensions to three. The performers on Lakmé felt more like real performers in a real space than like a portrait. And when I played the Oscar Petersen Trio’s Return Engagement I noticed several dramatic improvements. Dynamic transients sounded 10–20% bigger, and the piano had much more inner detail and complexity and a richer, more distinct tonal balance. The bass was more powerful and much tighter.

“Images inflated from two dimensions to three.” The guy’s on acid; that’s the only explanation.

The reviewer is quite precise here: “Dynamic transients sounded 10–20% bigger.” Can we see measurements please?

Oh, the shelf costs $6,195. The feet another $2.200. But the reviewer has “about $100,000 worth of gear,” so it’s no big deal.

Tweet about this on TwitterShare on FacebookShare on Google+Share on LinkedInEmail this to someone