Archive for July 17th, 2009

What Is LPCM?

Linear pulse code modulation (LPCM) is a method of encoding audio information digitally. The term also refers collectively to formats using this method of encoding. The term PCM, though strictly more general, is often used to describe data encoded as LPCM.

Description

LPCM is a particular method of pulse code modulation which represents an audio waveform as a sequence of amplitude values recorded at a sequence of times.

LPCM specifies that the values stored are proportional to the amplitudes, rather than representing say the logarithm of the amplitude, or being related in some other manner (companding). In practice these values will be quantized.

Implementations

LPCM is the method of encoding generally used in conjunction with the WAV container format, the de facto standard for uncompressed audio on PCs. The term PCM and LPCM often refer explicitly to the format used in WAV files, though LPCM data may also be commonly stored in other formats such as AIFF. LPCM is further used for the lossless encoding of audio data in the compact disc Red Book standard. LPCM has been defined as a part of the DVD and Blu-ray standards. AES3 is a particular format using LPCM. Linear pulse code modulation is used by HDMI.

Standard sampling resolutions and rates

Common sample resolutions for LPCM are 8, 16, 20 or 24 bits per sample.

While two channels (stereo) is the most common format, some can support up to 8 audio channels (7.1 surround).

Common sampling frequencies are 48 kHz as used with DVD format videos, or 44.1 kHz as used in compact discs. Sampling frequencies of 96 kHz or 192 kHz can be used on some newer equipment, with the higher value equating to 6.144 megabit per second for two channels at 16-bit per sample value. The bitrate limit for LPCM audio on DVD-Video is also 6.144 Mbit/s, allowing 8 channels (7.1 surround) x 48 kHz x 16-bit per sample = 6144 kbit/s.

DVD standards

Most DVD players only support 48 kHz/16-bit capability. Only more high-end players have built-in 96 kHz/24-bit capabilities. The DVD-Audio standard supports 192 kHz/24-bit playback.

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What HDMI cable should I buy?

CNEL strongly recommends cheap HDMI cables widely available from online retailers instead of the expensive counterparts sold in your local electronics store.

Here’s why:

Expensive cables aren’t worth it
If you walk into your typical electronics store to buy an HDMI cable, you’re likely to see prices upward of $50 with promises of better performance and faster speeds. Do you really need to spend that much money on a single HDMI cable?

Absolutely not–those cables are a rip-off. You should never pay more than $20 for a standard six-foot HDMI cable. And despite what salesmen and manufacturers might tell you, there’s no meaningful difference between the $20 cable and the $50 cable. Unless you see something obvious, such as dropouts or a flashing screen, the digital information transmitted by both cables is exactly the same–no cable can make the picture any better or any worse. We’ve used cables from many different companies in the past–such as Belkin, Accell, Monster,Knoxed, and SimplayHD–and have not run into any consistent issues with any brand of cable. With working cables and solid connections, we’ve seen no dropouts and “sparklies”–just consistent, dependable, high-quality audio and video. It’s that simple.

The editors at CNEL are so confident that cheap HDMI cables offer identical performance, we’ve been using inexpensive knoxed HDMI cables in the CNEL Home Theater Lab for more than a year with no issues. That’s saying a lot, especially when you consider that our video experts are constantly swapping in new products and changing configurations, which means our cables take much more abuse than they would in a normal home theater. We’re also accustomed to making long cable runs, and many of our cables from Knoxed are 15 feet long. We also use even longer 20-foot cables from a generic maker with no appreciable loss in video quality. If cheap HDMI cables are good enough for the eagle-eyed video professionals at CNEL we’re betting they’re good enough for your home theater.

And don’t get hung about other cables that offer a lifetime guarantee, protecting you in case your cables are technologically obsolete in the future. If in a few years there are consumer video products that output higher-than-1080p video signals (an admittedly unlikely scenario), you can always buy another cheap $20 cable online that can handle more data. And you’ve still saved yourself $30 over that $50 cable in the store.

Cheap HDMI cable sound great! Where can I get them?
The best way to score a cheap HDMI cable is to order over the Internet.

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