Axiom Home Page Forums General Discussion The Water Cooler hertz, bits, and bitrates - demistifying the devil

can anyone here point me to a link, or explain in plain english, what each of these really means in audio terms?

I know hertz is the sampling rate. 96kHz means every second there are 96,000 samples of the sine wave. but what about bits?

and bitrate? I know in computer terms bitrate is the # of bits streamed per second, but what is its relationship in audio and its relationship with bits and hertz?

I also know 24 bit will give you better sound than 16 bit, but why exactly? what exactly is 24bit? is it that each sample, all 96,000 of them are stored in 24 bit rather than 16, giving it even more definition?

if so, is bitrate an equation of hertz and bits?

thanks for all your replies!

Ravi,

I don't think you've got "Hertz" quite right. These may help.

Hertz

Bit

Bit Rate

Yeah, what Ajax said.

Hertz applies to the analog waveform of the sound and is independent of sampling.

Actually, the "sampling rate" is measured in hertz - as the sampling rate used for compact discs is 44.1 kHz (44,100 cycles per second or, samples per second). The sampling rate must be at least twice the maximum frequency to be reproduced.

So for a CD to reproduce audio up to 20 kHz theorectically requires a sampling rate of 40 kHz The actual standard is set at 44.1 kHz.

You are correct regarding sound. But it also applies beyond sound, into other areas of physics.

thanks everyone, that makes much more sense.

this does apply to my job as well, in a sense, as the company i work for sells digital systems to monitor brain waves. thus, i hear about bits and sampling frequency all the time.

thanks for the links

very helpful and pretty simple to grasp

I was not aware that "sampling rate" was measured in Hertz. Do you think the fact that I don't even know what "sampling rate" is could have anything do do with that? DUH! Thanks, BBIBH.

I'm so old that, when I first started learning about audio, there was no such thing as Hertz or Hertzian waves. Back in the dark ages they were called "cycles" or "cps" (cycles per second).

Well, I guess the important thing is that we are all open to learning!

I myself have spent many years in audio, and at one point was the boards "audiophile snob", and I am only just learning home theatre!

Just to add a bit(sorry)more, Ravi, the bit rate is essentially a combination of bits and sampling rate. On CDs the sampling of the frequencies takes place at 44,100 times a second, and as BigBear pointed out, this allows frequencies up to half of that(i.e. 22.05KHz) to be sampled perfectly(it's called the Nyquist theorem). The 16 bits (BInary digiTS) long "words" composed of 1s and 0s can allow for 65,536 different volume levels(2 to the 16th power)for each frequency sampled. So, the sampling measures the frequency and the particular combination of bits needed to represent the volume that frequency had in the original performance taken together result in an exact reproduction of what was originally recorded.

No, 24 bit doesn't necessarily give audibly better sound than 16 bit. Yes, each sample is composed of 24 rather than 16 bits and allows for over 16 million(2 to the 24th power)different sound levels. 16 bits allows for a dynamic range of about 98dB(6.02n + 1.76)while 24 bits would allow about 146dB in theory. However, this actually can't be used and recordings don't have at most more than about a 90dB dynamic range(e.g. the 30dB noise level of a very quiet room up to a 120dB maximum level at orchestral peaks). The quality of sound depends on the original recording technique and the mixing and mastering then applied, rather than whether it winds up on a CD, DVD-A or SACD.

JohnK, excellent post once again.

This really brings up the question as to whether 129khz recordings sound any better. I have found, however, that DVD's at 96/24 sound better than CD's at 44/16, but that may jsut be because the master recordings were better.

Patricia Barber's Modern Cool CD is only in 44/16 but its master tapes were 24bit, i assume.

So maybe one day there will be a digital format offering 256/32 but no one will hear the difference