Fitting 1 hour onto a CDr

[steve]

I just recorded 5 minutes and exported that as a WAV... 50Mb! If it is a fair test... that would exptrapolate to 600Mb for 1 hour!

That's right - about 10MB per minute.

What about those other settings in the WAV Quality window like dithering settings and rate converters?

The dithering settings are to do with converting from one format to another - this only affects "quality vs. speed" of the conversion. It has no effect on the final file size.

The "Sample Rate" is how many samples per second are used to represent an analogue waveform digitally - the more samples per second, the larger the file size will be, but the finer the representation of frequency will be, thus allowing higher frequencies to be recorded.
The "Sample format" is another term for "bit depth" and is the number of bits (binary digits) that are used for each sample - the greater the number of bits, the bigger the file size, but the greater the amplitude resolution, thus allowing a greater dynamic range (SNR).

CD's use 44.1 kHz and 16 bit - which is considered to be good enough for home listening. Professional audio is always done with higher sample rates and more bits per sample (for example 48 kHz, 24 bit is very common), but if the recording ends up on a CD, it must be "downsampled to 44.1 / 16 as that is the only valid format for a regular audio CD.

A more complete explanation of digital audio can be found here: http://en.wikipedia.org/wiki/Digital_audio

[Larbo]

Hi guys, I did my recording this week and it went exactly as you had predicted- 630Mb, fit beautifully on a single CD-r. I also found out that my sound card's software EQ affects the input (as well as the output) so I should have diasabled the card's audio panel while recording. In reality, I left it on and created an Audacity EQ ID with very slight enhancement at 20Hz and 15KHz (lowest and highest bands). Yes, I am a tweaker to a fault at times.

I was earlier mistaken in that I thought that I had 1.3 (hence being in the 1.3 forum) but my lack of FLAC certainly gave me up as a 1.2'er. Sorry.

My earlier questions about options such as dithering lead me to this inquiry.... Since these will all end up being burned on CD, do the various enhancement options end up with no net gain in sound quality if burned on a CD afterall... or do some audible benefits remain? Specifically,

1. Dithering- does this quality vs. speed setting matter when saving a new file and/or exporting to any format, i.e.- WAV or MP3?

2. Sample rates and format- If utilized, they will increase the file size and quality of the recording. However, when burned in an CD Audio format, will the file sizes shrink due to their being modified to a 44.1KHz/16-bit format?

Thanks again, Lar

[steve]

As far as I know, the "Real time" quality settings are only used if audio is being played back with a different sample rate to the actual format of the recording. For example, if you have the project rate set to 48000 Hz and have a track which is recorded at 22000 Hz, then the recorded track will be converted on the fly (in real time) to the project rate when you play the track. Using the fast settings in the preferences will allow it to do so with less processor over-head, but will sound slightly lower quality than using the high quality settings(probably not noticeable though).

When you come to mixing tracks or exporting the audio, the computer does not have to do this in real time, so the high quality settings should be used.

The increased processing time of the high quality settings is hardly noticeable when exporting, but does make a marginal difference when you are playing multiple tracks.

When exporting as MP3, there is always a trade off between file size and quality. You should select the settings according to how high you want the quality to be. Generally it is better to err on the high quality side as you can always reduce the quality later if you need a smaller size, but you cannot improve the sound quality be re-encoding to a larger file size.

A "high definition" audio file (say 96000 Hz 24 bit) will shrink considerably when converted to 44100 Hz 16 bit. Dithering will make no difference to the file size, but will allow a marginal improvement to the perceived sound quality when down sampling (going from a high bit depth to a lower one). It is easier to understand what dithering does if you consider the case of dithering switched off. Without dithering, converting from say 24 bit samples to 16 bit samples will simply ignore the unused least significant bits, that is, it will simply chop off the last 8 binary digits. This may lead to a slight crackling sound when listening to very quiet bits. What dithering does is to introduce just a little "noise" that smooths out these transitions, and the increased noise level is usually less obtrusive than the crackle.