Crash course in Bits

[cc1091]

Another thread I was reading brought to mind a question that has not been clearly answered for me. Back in 1988 or so, I bought a Denon CD player with "24Bit Oversampling". This was during the time when CD players were progressing from 4bit to 8 bit to ..24 bit oversampling.

Then suddenly, the jargon changed. Suddenly 24 bit oversampling was "inferior" (or so I was told) to single bit players using things like MASH filters. For the longest time, no one seemed concerned about how many bits of resolution a CD player had. Now suddenly formats like 24/96 and the like are all the rage.

Listening to my old Denon cd player, then placing the same disk in my dual tray Phillips CD recorder/player. I can hear a big difference. While the Phillips shows off every pitch very cleanly, the Denon is much more musical and (vinyl) record like. Of the two I prefer the Denon.

My question is this: What is the difference between the 24 bit oversampling that my old Denon uses and the latest formats? Is there any (especially after I route the digital output to my receiver's internal digital decoders)?

This message has been edited by cc1091 on 04-11-2002 at 12:11 AM

[boa12]

actually if you run a dts dvd on a regular dvd video player u should get around 75kbps for audio.

far superior to dolby usually running around 45k there.

all i know is to get the freq level divide by 2 (something to do w/ we having 2 ears i think).

so at 75k you're getting freq of 37.5khz & around 22.5khz w/ dolby dvd.

both above our hearing potential but the dts just feel more dynamic & titilating on the highs to me. guess the key word is feel & i think therefore would come into the pychoacoustics realm.

i think pcm cds are encoded 16 bit max in quantization. don't know on the oversampling processor you have cc.

but now we have hdcd, dvd-audio & sacd w/ their proprietary formats because of the disk space required

(even though normal dvd will hold 7 times+ more data than the regular pcm cd).

but as far as resolution, I hope to experience 96/24 w/ my regular dvd video player when i get this new queen in dts 96/24 format (on pre-order at www.dvdplanet.com ).

to get 192/24 you definitely need dvd-audio or sacd tech. maybe hdcd?

b

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This message has been edited by boa12 on 04-11-2002 at 12:54 AM

[Trooper]

Whoa there! Looks like major confusion in the bits and sampling rate arena.

cc1091, I think you mean 4, 8 and 24 times oversampling (sometimes just written as "24x oversampling"). Oversampling is a way to move the digital noise and artifacts far out of the audio band. CDs have a sampling rate of 44.1kHz and early players required a steep analog filter to filter out the noise above 20kHz. This caused it's own sonic problems. By oversampling and moving the noise further out of the audible band the output filters become much simpler and have much less effect on the audio. Make any sense?

Now on to bits. CDs are 16 bit. Using Digital-to-analog converters with higher bit capability results in higher performance and lower noise output. Most D/A integrated circuits (ICs) have actually become 1-bit converters with performance equal to or better than 20 or 24 bit converters. A few years ago someone demonstrated to me the audible difference between a "real" 18-bit converter and a 1-bit converter (with 18-bit performance). 1-bit converters have much better low level linearity. This is both measurable and audible (very audible with the right test tones).

Sampling rates must be at least 2x the highest frequency you want to reproduce. Theoretically a CD recorded at 44.1kHz can reproduce sound up to 22.05kHz. I believe DD and DTS are both sampled at 48kHz (not to be confused with their bit rates Boa12). The sampling rate is based on Nyquist's theorem regarding aliasing/anti-aliasing.

Pretty complicated topics, hope this helps (or at least doesn't hurt).

[boa12]

great info trooper. welcome. been awhile since i researched that sampling, bit rate & bits (quant) stuff & most of it left quickly .

sorry but guess i jumped right to bit rate as in what the player displays in kbps. so you're saying the dynamics increase w/ higher bit rates (given the dacs to handle it) but with ALL dvd video & pcm cd they're limited to 24khz & 22khz max freq extension?

i understand oversampling is a procees beyond sampling & done by the player. i've never had anything but a regular cd & dvd-video player so bear w/ me.

if you could, what is the definition of audio resolution? what is the relationship between the bit rate as displayed by the player & sampling rate as displayed by the processor (dacs)? besides the sample rate for the recording, i guess the sample rate of the dacs can't exceed that.

obviously, higher quantity encoded (16, 20, 24bit) result in higher sampling rates (speed). but if i get a higher bit rate on my player like say 75k w/ dts dvd, why does it sound so much more dynamic than a dolby disk (at around 45k) even though the processor sampling rate shows 48k for both?

does a dvd video never produce frequencies above 24k (sampling rate/2), or is a higher bit rate like 75k w/ dts actually producing a higher sampling rate than 48k (even though the processor shows only 48k)?

sorry for all the ?s. can't find the audio resolution bootcamp info anywhere. maybe just a good link will do.

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This message has been edited by boa12 on 04-11-2002 at 01:16 PM

[Trooper]

Higher bit rates, such as 75kbps, just means more information/less data compression. DTS is a higher bit rate because it uses less compression (vs. DD).

CDs are limited to a theoretical 22.05kHz and standard DD/DTS DVDs are limited to 24kHz.

Audio resolution is is the numer of bits (16, 24, etc.) This basically dictates the dynamic range and signal to noise ratio capability as well as the "preciseness" of each sample to the original analog signal. More bits = better.

I'm not that familiar with the bit rate displayed by the DVD player so I can't quickly speak to it's relationship to the sample rate although it would seem they would be directly related whereas a doubling of the sample rate should double the bit rate.

The DACs are at the mercy of whatever signal they receive when it comes to sample rate. They will default to whatever is coming from the player.

A higher number of bits (16,18,24) is not related to sample rate/sampling speed. It is related to bit rate (75kbps). So the difference you hear between DTS @ 75kbps and DD @ 45kbps has nothing to do with sample rate (which is always 48kHz) and everything to do with the bit rate which is higher because DTS uses less compression.

A video DVD (not including a 24bit/96khz type) will not produce anything over 24kHz whether it's standard pcm (actually 22.05khz), DTS or DD.

Even if you play a 24/96 disc your player may well output it at 48kHz. With this you would get the benefit of more bits (resolution) but not the higher sampling rate (HF extension).

[boa12]

thanks much trooper, just the info I needed. & thanks cc for bringing this up. I found my info source & they did say that the freq extension was determined by bit rate/2 - obviously wrong & means the "audio experts" are struggling w/ the conversion of computer tech into the audio world.

so apparently then dts w/ it's higher bit rate production allows for less information loss than dolby compression. unless somebody else can explain why dts just sounds more dynamic (& don't think it's psycho ).

i've got this new queen audio only dts 96/24 coming soon & will check out the display specs & sound. curious how it'll do on this regular dvd video player.

maybe if I wait long enough the recording tech will get so good i'll never need my combo dvd-audio/sacd/hdcd player.

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This message has been edited by boa12 on 04-11-2002 at 03:24 PM

[Seb]

remember Dolby and DTS are two compressed audio format, so the efficiency of the compression algorithms used will influence the results greatly.

I don't know which format is more efficient, but I do think DTS sounds better, whether it's due to the higher bitrate (and thus potential for more info to be in the signal) or to a more efficient compression scheme.

A question I've always had: is there a way to tell, or is there a list somewhere of the movies that were released with the older, more memory-gobbling high DTS bitrate, because apparently they are all released now with the lower bitrate version. Would be interesting to do an apples to oranges comparison to determine how much more/less bitrate influences the signal when using the same compression scheme...

I'm guessing the higher bitrate of those films would show up on the DVD player's bitrate display, however that may not be true, as the video might have taken the place of the audio (unfortunately) and since most DVD players only have one disply for both audio and video... Also, I don't feel like going through my (still relatively small) whole DVD collection to find out... Anyone?

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http://www.dvdprofiler.com/mc.asp?alias=Sebdavid - go laugh at my puny little DVD collection

[boa12]

seb, what is your dvdp (sony?) & what does it show? my old sony C650D video player shows video in mbps & audio in kbps seperately. also shows bit rate history & layer info.

oh & back to oversampling. i'm remembering some that oversampling was to verify info (prevent loss) but in most cases didn't improve audio quality - iow it usually is correct after the 1st or 2nd samples.

thought they were saying something like 16X was unnecessary unless in a car going down a torture track.

then again this is probably completely dif from oversampling quantity (X vs bits).

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This message has been edited by boa12 on 04-11-2002 at 08:31 PM

[Seb]

I have a Toshiba, SD1600 I think.

It only shows one bitrate, for both audio and video I guess.

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[boa12]

seb, prob just video as the 2 really differ, like mega vs kilo & there's no direct relationship i think.

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[m00n]

After reading this, this is what m00n hears

blah blah blah blah blah

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m00n

[boa12]

moon, i thought you said computer stuff was your thang.

same thing - digital tech. should be fine til we get to the dacs anyway.

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My Home Systems Page

[m00n]

Sure, I know what a bits and bytes are, but, oversampling this, MASH filters that, digital to analog converters... ACK!

I am a software guy not a hardware guy. And non of that bit twiddling assembly language either. I prefer my software languages much heigher level.

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m00n

This message has been edited by m00n on 04-12-2002 at 12:27 AM

[Seb]

you may be right boa.

I'll look in my player's manual, if I can find it.

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[boa12]

or seb like you say it could be a total of the video & audio into one grand figure, but don't know as again i'm over my head here.

if i remember, my dts on video tends to be around 4-10 mbps and audio right at about 75kbps.

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[Deang]

don't forget about all this fun stuff!!

http://www.onhifi.com/features/20010301.htm

http://www.aslgroup.com/dcs/upandover.htm

http://www.stereophile.com/showarchives.cgi?344

think I'll go back to a turntable!!

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Deanf>s>

Cary AE-25 Super Amp

Sonic Frontiers Line 1

Sony SCD-C555ES

Marantz DV-7010

Klipsch RF7's

Klipsch LF-10

MIT/Monsters

Toshiba 36"f>s>

Inside every small problem is a large problem struggling to get outf>s>c>-- 2nd Law of Blissful Ignorancef>s>c>

[cc1091]

Thanks Boa and Trooper. I think you have sufficiently hashed this subject out for me. Not sure how much of the info I actually understood, but further analysis will help me catch up to that curve.

I still wonder this:

Why does my old 1988 vintage Denon (DCD 1500-II) cd player with 24 bit oversampling sound better than my Phillips CDR765? In fact, why does this older CD player sound better than almost any of the CD players that I have been able to get into my home for a listening?

[Seb]

just for whoever may have been curious:

dug out the manual for my SD-1600, turns out the display is a sum of th audio, video, and subtitle on the DVD.

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[boa12]

seb & the video must be about about all of that figure.

cc, i'd help you if you could.

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[imel96]

<trooper>

Higher bit rates, such as 75kbps, just means more information/less data compression. DTS is a higher bit rate because it uses less compression (vs. DD).

CDs are limited to a theoretical 22.05kHz and standard DD/DTS DVDs are limited to 24kHz.

</trooper>

lets remove doubts and confusions. first paragraph is about bit rate and the second is about max freq.

best is just to give cdda numbers:

bit rate: 16-bit * 44k sample rate * 2 channel = 1411200bps or 1411.2kbps or 172 KBps

172KBps is the base factor for cdrom drive, so a 2x cd drive has 344KBps max transfer rate.

from nyquist's theorem the highest freq available from 44khz signal rate is 22.05kHz.

16-bit/24-bit differs in a lot like in amount of color showed on a computer monitor. more bits, more colors.

i don't know why they're not doing hdcd for computer monitors, that way maybe we could see 20-bit colors with 16-bit memory use, no?

the bits should form a sound wave form, like a sound wave. i'm not sure, but at least in .au signed format, the bytes 0 1 0 -1 0 1 0 in 44khz should make a 11khz tone with the lowest sound level. 1 -1 1 -1 1 should make a 22khz tone. to make a 11khz tone for one second, write 010-1 11000 times and feed them to a dac. i've never seen direct stream digital (dsd), sony claims it has different encoding.

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imel