For the podcast I’m recording [How the Tiger got her Stripes…so to speak], I’m including a few details on the settings I record and edit with and why. My research on what each number means is a bit rusty, so I’m giving myself a brief refresher course on How Digital Recording.
My digital recorder is set for 24-bit depth, 48 kHz sample rate, and .wav uncompressed format. My stereo microphones, indeed my entire chain, were all selected for the lowest noise floor I could get. Why? Because less noise…allows me to make more noise. Lets keep going, cause that really does make sense in a couple of minutes!
Why record at 24-bit depth? Especially since Audacity only edits at 16, and the final Audible file will be at 16 as well. Well, where I really need the extra dynamic range & excellent signal-to-noise ratio, is in the actual recording process. Having the room to be ‘too loud’ and not clip, or ‘too soft’ and have clean sound I can boost in post, means far fewer technical issues to go back and re-record. Instead, I can fix these problems in post production. Recording at 24 means retaining a clean too-loud, retaining a clean too-soft, with best overall signal-to-noise ratio my machine can give me. I’m a dynamic performer, so this is important to me.
The extra headroom provided by 24-bit can also be heard as physical soundspace in which recording was made – and this sense of physical presence matters hugely to me. I want to sound like a real person, not a flat voice emerging out of a void. This is the same logic behind retaining most inhales and subtle mouth noises in my performances – I want to sound like a real person reading to you, performing for you. I carefully plan breaths and subtle noises into the performance – they are never random; they are all intentional.
This style decision is pretty controversial – either you love it or you hate it :) I’ve had more than one fan write to me saying, ‘You have ruined me for all other audiobooks! No one breathes! You can’t hear the soundspace! Other books all sound airless!’ This gives me non-malicious glee. Yes – this is what I intend as a producer. Similarly non-fans have written exhorting me to edit for god’s sake! not realizing that the final product is edited to within an inch of its life and retains indicators that a real person read the book, on purpose. Anyone with an ear for editing or knowledge of production or the experience of listening to a thousand audiobooks can hear the careful editing. The difference between untutored ‘real sounds’ recording and what I do is vast – but I can appreciate that at first glance one could make that snap judgement, or just dislike the result, no matter how polished.
So! What are the technical advantages of that 24 bit depth, that allow these performance elements to shine in the recording?
From: Sample Rate and Bitrate: The Guts of Digital Audio by Dan Connor
In general, the higher bitrate the ‘smoother’ the sound will be. 8-bit sounds rather grainy and harsh whereas 16-bit sound sounds quite a bit better. 24-bit sound is used by most audio professionals these days not because it sounds so much better than 16-bit sound but because the higher accuracy is useful because so much is done to the audio in the recording, mixing, and mastering process. Higher bitrate means that each change that is done to the sound produces a more accurate result. Imagine only being able to describe the sounds you’re recording with two volumes: on or off. It would be impossible to produce any music at all with such a low bitrate.
I record and edit at 48kHz sample rate. Why record sounds literally above the range of the human ear? Here’s a great explanation – one that my ear agrees with:
From: 16 Bit vs. 24 Bit Audio by The Tweak (tweakheadz.com)
Nyquist Theory and Sample Rate
This theory is that the actual upper threshold of a piece of digital audio will top out at half the sample rate. So if you are recording at 44.1, the highest frequencies generated will be around 22kHz. That is 2khz higher than the typical human with excellent hearing can hear. Now we get into the real voodoo. Audiophiles have claimed since the beginning of digital audio that vinyl records on an analog system sound better than digital audio. Indeed, you can find evidence that analog recording and playback equipment can be measured up to 50khz, over twice our threshold of hearing. Here’s the great mystery. The theory is that audio energy, even though we don’t hear it, exists as has an effect on the lower frequencies we do hear. Back to the Nyquist theory, a 96khz sample rate will translate into potential audio output at 48khz, not too far from the finest analog sound reproduction. This leads one to surmise that the same principle is at work. The audio is improved in a threshold we cannot perceive and it makes what we can hear “better”. Like I said, it’s voodoo.
Pretty cool, eh?
In the end, everything I record is down-sampled *sigh*. Audible’s file parameters are 16 bit, 41kHz, 192kbs compressed MP3s. (here insert an entire soliloquy full of pathos bewailing MP3 compression losses) They might even convert to mono – I don’t have the heart to check :) So why go to all the trouble? Because the more detailed and cleaner the original raw data, the more fidelity you retain even after effects, editing & processing. I have such lovely hardware – I’m willing to go to the trouble to use software settings that let the warm, detailed, sympathetic signal shine.
This makes me happy all on its own! But the end result of beautiful audiobooks for you to listen to, and to attract new authors to employ my talent and skills – well, that’s the name of the game :)