Is there a list somewhere of "standard" encoding rates? I know, for example, CDs are encoded at 44100, as is a lot of digital sound, but I've seen programs that specify different levels of quality (like radio, phone, tape, CD) and I'd like to know if there are some encoding rates that are accepted as standardized for recording at different levels of quality. If so, is there some place I can get a list of them? Thanks! Hal
On Tue, Apr 05, 2005 at 02:26:03AM -0500, Hal Vaughan wrote:> Is there a list somewhere of "standard" encoding rates? I know, for example, > CDs are encoded at 44100, as is a lot of digital sound, but I've seen > programs that specify different levels of quality (like radio, phone, tape, > CD) and I'd like to know if there are some encoding rates that are accepted > as standardized for recording at different levels of quality.Well, where analog formats are concerned these are estimates, and in there is no *standard*. "CD quality" is 44100 Hz stereo with 16 bits per channel. FM radio is limited to 17 kHz iirc, so in theory you could sample at 32 kHz, but in practice people usually use 44.1 or 48 kHz and just lowpass filter. AM radio is lower quality (mono) but I don't know what the digital equivalent would be. Telephone is nominally 8 kHz mono (i.e. really bad) though I think the use of digital voice codecs in the last 20 years may have improved on this a bit. Maybe someone else can comment on tape fidelity. I think the issue there has more to do with recording artefacts than bandwidth. FWIW, -r
Ralph Giles <giles@xiph.org> writes:> On Tue, Apr 05, 2005 at 02:26:03AM -0500, Hal Vaughan wrote: > > > Is there a list somewhere of "standard" encoding rates? I know, for example, > > CDs are encoded at 44100, as is a lot of digital sound, but I've seen > > programs that specify different levels of quality (like radio, phone, tape, > > CD) and I'd like to know if there are some encoding rates that are accepted > > as standardized for recording at different levels of quality. > > Well, where analog formats are concerned these are estimates, and in > there is no *standard*. "CD quality" is 44100 Hz stereo with 16 bits per > channel. FM radio is limited to 17 kHz iirc, so in theory you could > sample at 32 kHz, but in practice people usually use 44.1 or 48 kHz and > just lowpass filter. AM radio is lower quality (mono) but I don't know > what the digital equivalent would be. Telephone is nominally 8 kHz mono > (i.e. really bad) though I think the use of digital voice codecs in the > last 20 years may have improved on this a bit. > > Maybe someone else can comment on tape fidelity. I think the issue there > has more to do with recording artefacts than bandwidth.Typical sample rates for music is 32, 44.1, 48, 96 and 192 kHz. FM radio is limited to 15, not 17, kHz so 32 kHz is an adequate sample rate for such broadcasts. But, as already stated, it's common to sample in 44.1 or 48 kHz, although in that case you should make sure you notch out 19 kHz. Hard. Otherwise you'll sample the stereo sync tone as well. It's already filtered with -60 dB (approx) in the reciever, but even so it might add information that makes it harder to compress the material. Also, FM-recievings usually contains a lot of high frequency artefacts that will make it hard for flac to work efficiently. If you can't filter these things out, I'd recommend 32 kHz. Tape can reach anything from 14 to 24 kHz (lousy recordings might have even lower quality than 14 kHz, of course) but as an general rule I'd say that 32 kHz sample rate is sufficient if we're talking normal tapes. Chrome and metal tapes might be a reason to use higher sample rates (depending on the equipment), or, of course, sheer lazyness. Except from noise there shouldn't be any need for filtering anything out. Reel-to-reel-tapes on higher speeds easily mark 20 kHz so there a high sample rate is a good thing. AM-broadcast is limited to 4.5 kHz. That means that 8 kHz sample frequency might filter out some of the bandwidth, but I doubt you'll notice much difference considering the crappy signal to begin with. If you do, use 11.025 or 16 kHz sample rate. LP:s etc are usually limited to 16 kHz in the mastering, so there's no real point sampling those at higher rate as 32 kHz as well. Also, they're usually gradually going from stereo to mono between 150 to 50 Hz so if you can "monoify" the signal from 50 Hz and down you'll also filter the rumble (it's in 180? phase between the channels) which also will improve the possibility to compress the material, aside from the possibility to play it back LOUD without wasting amplifier power or risk the speakers. In general; use your ears. If you can't hear the difference, does it matter...? -- Martin Persson martin@kfib.org http://ss.kfib.org/ Friendly fire isn't.
On Tuesday 05 April 2005 11:26 am, Ralph Giles wrote:> On Tue, Apr 05, 2005 at 02:26:03AM -0500, Hal Vaughan wrote: > > Is there a list somewhere of "standard" encoding rates? I know, for > > example, CDs are encoded at 44100, as is a lot of digital sound, but I've > > seen programs that specify different levels of quality (like radio, > > phone, tape, CD) and I'd like to know if there are some encoding rates > > that are accepted as standardized for recording at different levels of > > quality. > > Well, where analog formats are concerned these are estimates, and in > there is no *standard*. "CD quality" is 44100 Hz stereo with 16 bits per > channel. FM radio is limited to 17 kHz iirc, so in theory you could > sample at 32 kHz, but in practice people usually use 44.1 or 48 kHz and > just lowpass filter. AM radio is lower quality (mono) but I don't know > what the digital equivalent would be. Telephone is nominally 8 kHz mono > (i.e. really bad) though I think the use of digital voice codecs in the > last 20 years may have improved on this a bit. > > Maybe someone else can comment on tape fidelity. I think the issue there > has more to do with recording artefacts than bandwidth. > > FWIW, > -rThe numbers are helpful, but I was trying to use those terms as examples. ?I guess I mean, are there encoding rates that are more or less standard? ?For example, if an expert is recording at a lower quality, are they likely to set it at, say, 10000 samples per second, or more likely to use 8000 samples per second? ?Or are there no standard rates and most files are just encrypted at whatever rate the person creating them felt was a good balance of quality vs. file size? Does that make sense? Hal
On Tue, Apr 05, 2005 at 10:44:41AM -0500, Hal Vaughan wrote:> The numbers are helpful, but I was trying to use those terms as examples. I > guess I mean, are there encoding rates that are more or less standard? For > example, if an expert is recording at a lower quality, are they likely to set > it at, say, 10000 samples per second, or more likely to use 8000 samples per > second? Or are there no standard rates and most files are just encrypted at > whatever rate the person creating them felt was a good balance of quality vs. > file size?If you just want digital sampling conventions, there are generally two. One based on subdivisions or multiples of the CD rate of 44100 Hz and one on powers of two. So, as mentioned, 44.1, 48, 96 kHz are common for music. On the low end, 32, 16, 8, and 11.025, 22.050, and sometimes 24 are common. Those two sets give you something close to most targets. A lot of it depends on your target hardware capabilities. HTH, -r
On Tue, Apr 05, 2005 at 08:26:45AM -0700, Ralph Giles wrote:> AM radio is lower quality (mono) but I don't know > what the digital equivalent would be.Just a minor nit-pick: AM radio can be stereo. However its use is almost nonexistent. See <http://users.hfx.eastlink.ca/~amstereo/amstereo.htm> for more information.> Telephone is nominally 8 kHz mono > (i.e. really bad) though I think the use of digital voice codecs in the > last 20 years may have improved on this a bit.Telephone lines (POTS) have a frequency range of 300-3400Hz. That means 7kHz mono should be enough, although 8kHz is generous towards the transition bandwidth/roll-off. - Andrew