Tuesday, November 30, 2004

How is DSD different?

Direct Stream Digital (DSD) is different from Pulse Code Modulation (PCM). The most obvious difference is the sample size: 1 bit vs. 16 for CD or 20 to 24 for DVD. But there’s more: if you send the raw data stream out to a speaker, with PCM you get random garbage. With DSD you get an intelligible audio signal which bears a striking resemblence to the actual sounds recorded. This is because the 1-bit samples are naturally grouped into understandable patterns, whereas with PCM they are numbers, decodible only by your player’s Digital-to-Analog (D/A) converter. I’ve aready mentioned other differences. Still Don’t believe me when I say SACD is better?

Oh, the superior sound of analog!

Most people don’t realize this, but the major defect of records, especially worn ones, is noise, not audio quality. Good records that are well-kept are able to reproduce sounds that CDs shudder to even attempt! This is because CDs need to be filtered so that no frequencies higher than, oh, 22 kHz or so, get accidentally recorded and wind up getting “aliased” as lower frequencies on playback. Records, on the other hand, are not digital. An exact groove is cut into the surface of the master, which is copied to make your record. If the record is well-maintained and high-quality playback equipment is used, any record will sound better than a CD of the same recording.


Saturday, November 27, 2004

Dual Disc: Wow, that’s disappointing.

At long last, DVD-A has now come out with their answer to SACD Hybrid—well, sort of. Instead of a dual-layered disc with different format on each layer, they chose double-sided instead. DVD content is on side A. CD content is on side B. What does this mean? No label to guide you to insert the disc in the correct way. Wasn’t it frustrating to have to read that little ring in the middle of a double-sided video DVD, just to make sure you were going to see the widescreen version instead of the “standard” one? Looks like once again, the DVD Forum has come out with too little, too late!

Wednesday, November 24, 2004

How does DSD work?

The answer is surprisingly simple. DSD is a patented noise-shaped version of Delta-Sigma modulation, a one-bit sampling process already in use by most multibit-sampling A/D converters. Sony and Philips have simply removed the intermediate step of turning the raw samples into numbers. Now, you know that digital recordings with smaller sample sizes usually have significantly more noise than those with larger sample sizes, but Sony and Philips have taken care of that with fifth-order noise shaping. I’ll probably discuss noise shaping another day.

Saturday, November 13, 2004

SACD is better than DVD-A.

Why do I say that? Well, the answer is really simple. More resolution horizontally (timewise). First of all, DSD, the format used by SACDs, can accurately represent frequencies of up to 100 kHz, even in multichannel mode. DVD-A format is primarily either PCM or Dolby Digital and only has its highest frequency response in 2-channel stereo, where its sampling rate is 192 kHz, allowing for frequencies only as high as, say, 90 kHz before response drops off dramatically. If 5.1-channel multichannel mode is used, that drops down to about 45 kHz. And news flash: stereo and multichannel never appear on the same audio DVD, so the stereo listener is at the mercy of the mixdown algorithm in the player. So much for DVD-A. SACD, on the other hand, has enough room and processor power to handle 6 channels of audio up to 100 kHz plus a premixed stereo downmix, also up to 100 kHz. You may not need to hear sounds that high, but it’s sure nice to know they’re there!

Tuesday, November 09, 2004

720p: The world’s finest?

During the Major League Baseball games on Fox Sports, I kept hearing the same line in their commercials for their own HDTV presentation of the games: “Presented in 720p: the world’s finest high definition standard.” But wait—I thought 1080i 1080p were the finest standards! What’s going on here?

For those uninitiated to Hi-Def, 720p means 720 lines, progressive scan. 1080i means 1080 lines, interlaced scan. 1080 is obviously a better picture than 720, so where do they get this “world’s finest” stuff? More frames per second? Less lossy compression? Or could it be progressive scan vs. interlaced scan? If anybody has the answer, please post a comment.

Monday, November 08, 2004

How do records get scratched?

Records get scratches because of

  1. how they're made,
  2. how they're played, and
  3. how they're kept.

Records are pressed into vinyl, a type of plastic. Vinyl is soft, so it's more easily scratched than other materials. Records are played with a stylus (called a needle, commonly) that tracks the groove and vibrates by the wave pattern recorded in it. If the tonearm of the player gets jostled, the needle will scrape across the surface of the record; and because the needle is made of diamond, it is a lot harder than the surface of the groove wall. Hence the scratch.

Records can also be harmed by dust and dirt that is not cleaned out of the grooves. Various cleaning kits are available, but remember to always follow the instructions, and never clean a vinyl record in the same manner as a CD!

Saturday, November 06, 2004

Not CD, SACD.

There’s a new digital audio medium out there, and it’s growing by leaps and bounds. It’s physically the same size as a CD and the same data size as a DVD, but it is neither. It’s called Super Audio Compact Disc, and it was developed by Philips and Sony, the inventors of the original CD format. SACD is the wave of the future: Hi-Res audio to the extreme. The digital data is sampled in individual bits, instead of pulse codes like PCM, at an industry-leading 2.8224 MHz. Why is this significant? Because the higher sample rate and the single-bit sample size mean more exact sound.

And there are also hybrid discs available. Hybrids have two layers: one for the SACD player, and one for those of us who still cannot afford one but have an ordinary CD player.

SACDs are a multichannel format, supporting up to 6 simultaneous discrete channels: 3 front, 2 rear, 1 subwoofer. Multichannel discs also come with a premixed stereo track for players that don’t have surround.

Check the Acoustic Sounds site for further info or to order SACDs.

Friday, November 05, 2004

Stereo is not just left and right.

Surprised? So was I when I found out. It turns out that most live recordings in stereo, including the old LPs, are recorded with three channels of audio first: Left, Right, and Center. Then when the final master is produced, the center channel is mixed to the left and right channels. For live 2-channel recording, see the binaural article below. But live stereo is recorded with 3 microphones. And now ya know... the rest of the story.

Thursday, November 04, 2004

Binaural? What’s that?

Surprising to me, most people haven’t even heard of the best audio presentation format available. “Bi-what?” they ask me. But binaural sound has been in existence for over 100 years, longer even than stereo. So what exactly is binaural?

It’s really simple, actually. Binaural (“by-nor'-all”) is the same logical format as stereo (left, right) with the functionality of surround sound in 3-D. This is all done by acoustics, so the format can be digital or analog, broadcast, closed circuit, or recording, and the spacial information is retained. It can be recorded on tape, record, CD, SACD, DVD, MP3, you name it.

Binaural sounds just like live, in-person when listened to with headphones. You hear sounds in front, behind, up, down, left, right, and everywhere in between. No decoding necessary. And it sounds just like surround on a surround decorder. How did they do that? How did they get vertical, horizontal, and front-to-back all in only two channels?

The answer lies in where they placed the microphones. To record or broadcast in binaural, you have to put the microphones the same distance apart as human ears: approximately 7 inches, and back-to-back. For best results, in most cases a dummy head or actual human head is used (the technician’s own head, for example), with the microphones placed just inside the outer ear. This acoustically processes the audio before it reaches the microphones, so when it is played back, the brain interprets the position, distance, size, and shape of the object creating the noise (an instrument, for example).

Surround sound is good, but binaural is better. For further information or to order binaural recordings, visit John Sunier at the Binaural Source.