Monday, February 15, 2010

The Future of Amplification

Recently there have been several positive reviews of the NAD M2 Direct Digital Amplifier (white paper). It is the first of its kind, and I expect many more amplifiers like this will follow.

Today most audio sources are digital: CD/SACD, DVD/Blu-Ray, HDTV, PC/MP3 server, etc. These signals are passed through a digital-to-analog converter, have volume control applied, and are passed as analog signals to the amplification stage. Even current class D amplifiers accept an analog signal, convert it to a PWM (pulse width modulation) digital signal, and use that to generate the final amplified analog signal sent to the speakers.

The NAD M2 is unique in keeping the input digital signals in the digital domain as long as possible. It accepts PCM (pulse code modulation) digital inputs, applies volume control digitally, and converts the PCM to PWM for output by the class D amplifier. Keeping the signal digital as long as possible eliminates all the possible noise sources in the redundant digital-to-analog-to-digital conversions, and the lossy analog connections between source, pre-amplifier and power amplifier.

(Yes, I deleted my previous audio post as I realized I was spreading disinformation. I am currently fascinated by the topic, and will keep trying.)


Unknown said...

Where does Sonos fit into this? I see them (or someone like them) as poised to disrupt midrange audio equipment.

I think of audio as roughly divided into 3 segments: crappy iPod players, home theaters, and sky's-the-limit audiophile systems.

Sonos initially appeared to be at the pricey end of crappy iPod players. But with the release of the Sonos Sub and PlayBar, they are seemingly moving upmarket.

Traditional home theater systems have great sound, but much of their cost is wasted on being in effect a giant switchboard among multiple discrete audio components (DVD, cable, etc.). They see digital services as just one more add-on, when in fact digital is a replacement for all the other components.

Traditional home theater also suffers the same dismal UI problems as other traditional AV component makers. I know someone whose kids are literally geniuses, per independent testing, yet have trouble switching between Apple TV and DVDs on their home AV system. Traditional AV seems mired in a wired, analog past.

This leaves a huge opportunity for somebody to do an all-digital, all-wifi, no-setup surround system. Playbar appears explicitly designed to facilitate replacing the AV system. You plug your AV inputs into your TV, and run the optical out to the Playbar. You run the whole thing from a tablet app.

I haven't tried PlayBar. Reviews say it's great, but it's hard to trust online audio reviews. Curious what you think.

Eric Rollins said...

I should have titled this post "the future of amplification, assuming people care most about sound quality". I'm not sure that is how things will play out. Right now I'm looking at Panasonic ending avalability of their plasma TVs. Not because they have been replaced by anything better, but because LCD looks brighter in rooms with the lights on at Best Buy.

Yes the home theatre receiver vendors do terrible user interfaces. And yes that is the most important factor for most consumers. The reasoning of the post still stands: it makes sense to only invest once in the best possible digital to analog converter, and have all components share it. Keep signals in the digital domain as long as possible, including applying volume control digitally.

I don't have personal experience with Sonos. I assume they do good user interfaces (and by supporting iTunes leave much of the problem to Apple). I see they do have a box to attach to a receiver, as well as all-in-one setups to drive their own speakers. These setups, including the soundbar, would have the usual drawbacks of sub-plus-satellite systems: the hole between the maximum frequency of the sub and the minimum frequency of the satellites. This matches a male voice, and is one reason why you end up raising the volume (and lowering it again because movies are mixed for deafening loud reference levels for explody parts).

Other configurations of parts is of course possible. Meridian speakers accept digital audio input over RJ45 cables and do the digital-to-analog conversion and amplification locally inside each speaker. Wireless extender kits are avaiable for speakers, though reviews so far rate them marginally acceptable audio-quality-wise for home theatre rear surround channels only. We haven't gotten to the home decorators nirvana yet: invisible, wireless, flush-on-wall speakers that sound as good as the big floorstanders of 20 years ago.

Unknown said...

I don't have experience with Sonos either, so I'm shooting in the dark a bit.

My reason for mentioning it here was to ask your opinion on their signal architecture, which stays in the digital domain as long as possible by converting to analog separately at each satellite speaker.

This brings up the point that in a multi-speaker system, it might be hard to reconcile the two goals of staying digital as long as possible, while using only one D/A converter.

That in turn made me think that if you could simplify enough -- that is, pull out enough extraneous non-D/A hardware out of that huge honkin' AV box under my TV -- you might make save enough to put good D/A in every satellite, thus staying digital all the way out to each satellite, and still have good sound quality. Just musing.

It appears that the Sonos 5.1 solution works that way. You buy one of their network bridges, and 4 separate WiFi/amp/speaker devices: one (stereo) PlayBar, one Sub, and two satellites. Connect them to your network, they set themselves up, and you're done.

I'm not pumping that product specifically -- don't really know a thing about it -- just wondering if that general architecture might make sense.

I may be hammer-nailing this, because our band, though still all analog, is slowly decentralizing amplification. We recently switched to powered main speakers, which decreased the total weight of our rig, while simultaneously increasing power output and sound quality. This made me wonder -- for months now -- if we could eventually go all digital, all Wifi, into powered speakers with integrated D/A. With that in mind, I saw Sonos recently and thought wow, that's it exactly.

Unknown said...

Update: bought a Sonos Play:5, just to see. They've been all the rage with SF millennial hipsters for a coupla years.

Audio quality is as expected -- upper end of crappy iPod players.

Setup is the selling point: go from sealed box to streaming music in about 5 minutes, controlled from any mobile device. Integrates well with all non-Apple streaming services, e.g. Spotify.

Surprisingly, Apple integration is bad: they don't support AirPlay, which in turn means you can't play anything from iCloud or iRadio without first downloading the content to a device on your own subnet. But if you download to your phone, for example, then your wife can't play it, even though she uses the same iCloud data store, because she hasn't downloaded it to her own device. That's a dealkiller for me, but many won't care.

Conclusion: things are changing too fast to contain wireless receiver, DAC, amp and speaker all in a single enclosure. It's not only the sound quality, but risk of being Betamaxed in some unexpected way.

Seems like you reduce your replacement rate by buying passive speakers that will last many years; separate amp that will last many years; and wireless receiver and DAC that you will replace every couple of years till things settle down.