Simplest form of my question: can one store more low-fidelity audio on a CDR than high-fidelity audio - assuming one wants to replay it on a traditional cd player (so we’re not talking about MP3 or compressed formats).
If the answer happens to be yes (which seems somewhat unlikely but possible…), then what is the maximum capacity (length?) that can be stored?
The question applies to storing spoken word (some dude recording his memoirs for personal collection) as opposed to storing typical high-fidelity music.
and please remember, the CDR can be played back only on a traditional c.d. player.
No, what you seek is impossible. A red book CD contains 700 MB of space, and will hold 80 minutes of two-channel stereo audio. This is the industry standard for all CDs and CD-Rs which are to be compatible with normal playback equipment. No way around it, either.
As fishbicycle said, the amount of data is fixed however if you lowered the sample rate then yes you could store more audio. But you would have to come up with your own sampling equipment and playback software.
Actually, the amount of data isn’t the problem, it’s the sample rate and bit depth that’s hard-coded in the hardware. (I think that’s what you meant, but at a lower resolution you can fit more sound in the same amount of data, which is what the OP was asking.)
The “red book” fishbicycle mentioned is the book in which the standards for audio CDs is defined. There are no allowances for sampling rates other than 44.1 kHz and bit depths other than 16 bits.
There’s some precedent for making non-standard audio CDs, but the companies that make them break the standard to embed DRM as opposed to shoving more audio on the disk. Your low-fidelity CDs would be unplayable on all existant players and you’d have to make some software (or, if you’re feeling especially technical, hardware) to play them. All in all, it’s easier to put MP3s on a data CD and buy a player that can handle that format.
CD Sample rate is 44.1 KHz - If you sample at, say, only 8KHz, it will still be audible - especially for unaccompanied spoken voice, but the quality will be noticeably poorer (it will sound like telephone or two way radio conversation).
You could probably drop down to 5KHz sampling rate or lower, and still be able to make out what it is you’re supposed to be hearing, but it would not be a pleasant listening experience for most people.
ETA: So all other things being equal, you should be able to fit about five times the play length on a CD, if you just used custom equipment with an 8KHz sampling rate, and you used the same methodologies for storing the data on the disc.
If he’s got spoken-word stuff, it’s best to use a codec specifically designed for it, like Speex. He’ll be able to fit much more audio in a given amount of disc space than if he had used MP3 at the same bitrate. Of course, few (if any) modern CD players support Speex, but that’s an issue only if one intends to play the file on a standalone CD player rather than a computer.
I don’t think there would be a problem, given the right software, of recording different things on the left and right stereo channel of an audio CD. That way, you’d be effectively doubling the length. You’d just have mono sound instead of stereo. You could play it back on any CD player that had a balance control or other way of selecting just one channel/speaker.
A relatively easy way to store more audio and still be able to play it back on normal equipment would be to record it a twice the speed (e.g. record to tape, then play back at twice the rate to record to CD). This has the advantage that the audio is accessible without any special equipment. My stepfather got records for the blind some 30 years ago. They were recorded at (IIRC) 16 2/3 RPM*, and he had a special record player that went that speed, but he played them back at 33 1/3 anyway. Perfectly listenable. (* or maybe recorded at 8 1/3 RPM, and played back at 16 2/3)
Another easy approach is to record separate audio on the left and right channels, (on preview, as Thudlow Boink mentioned). Between the two, you can get four times the audio on a normal CD that won’t require special playback equipment.
wow, I didn’t expect so much feedback on this topic, thanks all!
For everyone who seems curious, the specifications outlined in the OP were due to following reasons: the audio is an elderly gentlemen’s memoirs (20 hours+ I believe) that he apparently wishes to review. I am unfamiliar with his hardware setup but from my limited experience with the elderly, they often tend to have antiquated setups (i.e. if they have a stereo, they may well have a first gen ghetto blaster from the 80s). I hope that stereotype isn’t too offensive, but I feel confident in stating the that people 70+ years of age don’t typically have up to date hi-fi equipment (and this man apparently does not use computers). So CDs seemed like the most user-friendly approach. DVDs are appealing b/c of their capacity but considering that he likely has an old dvd-player it may not play MP3s either in which case the capacity of the DVD is moot.
The RIGHT-LEFT channel thing was a great suggestion, and I take it that would enable me to store 160 min per cd? so that is the max we’ve been able to figure out thus far? short of chipmunk ideas.
As Thudlow Boink suggests, you can record two different mono tracks on a CD, but you will need an audio mastering tool that can take two different mono tracks and assign them as Left and Right channels and produce a standard stereo signal. And, whoever plays this CD will need to have a way of turning off one channel or another for playback.
Audio CDs aren’t like four-track tape where you can lay down separate tracks at different times - it’s all-at-once with no going back. Actually, if universal playback ability wasn’t one of the criteria, I’d suggest four-track tape as one possibility for this project as pretty much every four-track deck I’ve seen makes it mindlessly easy to listen to just one track at a time.
Another possibility to look into is time compression of the spoken word. **fishbicycle ** can probably expand on this - the general idea is to speed up the speech without making the speaker sound like they’re on helium. It’s a pretty common technique used in producing commercials to cram as many words into 30 seconds while remaining intelligible. Whether it’s done by boosting the speed and dropping the pitch to compensate, or a digital shrinkage of silent spots, you might find a worthwhile reduction in time, especially with 20+ hours of source material.
May I ask why you are trying to minimize the number of CDs used? Individual CDs are extremely cheap, so using ten versus two is not going to save that much money. Storage space should not be a major issue either.
If this is just an interesting mental exercise, great! If you are looking to actually apply it, I would suggest that the effort to cram it in is not worth the savings or the effort to play the result (unless I’ve missed something here).