MasteringMixing

How to bounce audio for mastering, CD, digital download and more

How to bounce audio for mastering, CD, digital download and moreWhat does it mean to bounce audio?

In modern day digital audio, the term ‘bouncing’ or ‘exporting’ refers to the process of turning either some or all of the things that are going on in your session into an audio file. This could be a bounce of your finished song that you can then release on iTunes or stream on Spotify. Or it could be a bounce of your mix to send off for mastering.

The correct way to bounce audio can seem tricky at first. Which format, which sample rate and which bit depth to use are all common questions. In this lesson, we’ll cover all of this as well as explaining which file types to use, online vs offline bouncing and some of the other reasons you might want to bounce down the audio in your sessions.

Audio bounce settings:

When you’re ready to bounce your track, open your DAW’s bounce dialogue window. Here, you will be given different options to set different parameters for the file you’re about to create. These parameters include the file type, sample rate, bit depth, format and more. Let’s break down what each of these mean.

File Type:

File type lets you determine what the format of the audio file that you create will be. Options usually include WAV, AIFF, MP3 etc.

Sample Rate:

Sample rate refers to the number of samples per second that a piece of digital audio is made up of. This dictates the maximum frequency that can be represented.

Bit Depth:

Bit depth defines the number of values available to represent the amplitude of the samples, and in turn dictates the dynamic range.

Format:

For the format, you will be given options such as mono, multiple-mono, and stereo-interleaved. Stereo-interleaved gives you a stereo file. Multiple-mono gives you two separate mono files, one for the left channel and one for the right channel. Mono summed will give you a summed version of both the left and right channels in a single file.

Online (real time) / Offline Bounce:

An online bounce will export the song in real time i.e. it will take as long to bounce the audio as it would to listen to it from start to finish. Offline bouncing is much quicker as it does not happen in real time. Generally speaking, online bouncing is a more reliable way to bounce your audio. That’s because, when bouncing in real-time, the audio will play for you to listen to as the bounce happens. This gives you the opportunity to listen to what’s being bounced to make sure everything is as it should be. It gives you the opportunity to catch an error before it is too late.

Now, let’s look at how to set these parameters for some of the most common bouncing applications. Let’s start with the bouncing of your final mastered track.

How to bounce the final mastered track:

When deciding on the settings for the bounce of the final track, the options you choose are largely determined by what it is that you’re going to do with your finished songs. You may want to upload them to a digital distributor like Landr or CD Baby to make them available on platforms like iTunes and Spotify. You may also want to upload them directly to sites like Sound Cloud for people to download and stream. Or you may want to burn them to CD.

For a long time the standard for the bounce of the final track was a stereo interleaved, WAV format file with a 44.1kHz sample rate and a bit depth of 16 bit. The reason for this was that, for a long time, CDs were the most common way to distribute your music. To write a digital audio file to an audio CD, the file must be a PCM format (i.e. WAV or AIFF), stereo file with a sample rate of 44.1kHz and a bit depth of 16 bits.

Largely speaking, this remains the standard for the final bounce. However, as we move away from CD releases and towards streaming and digital downloads, you are now often able to release your songs to the world with a higher sample rate and a higher bit depth setting than the CD quality standard. Various platforms have their own recommendations for the sample rate and bit depth of the files that you upload.

So, should you bounce to a higher sample rate and bit depth if the platform you’re uploading to supports it?

Bouncing the final master above CD quality:

Well, there is plenty of debate as to whether bouncing a file with a sample rate higher than 44.1kHz and a bit depth higher than 16 bit produces a better sounding file. First, let’s look at what you’re getting with a CD quality file. A sample rate of 44.1kHz can reproduce frequencies up to 22.05kHz. A bit depth of 16 bit gives you a dynamic range of 96dB. Let’s put that into context… The highest frequency that human beings can hear is 20kHz, and most of us can only hear up to about 15 – 18kHz. As for dynamic range, even really dynamic music like classical generally only has a dynamic range of about 50dB at most. Rock and pop songs have far less.

Now, there are definitely reasons as to why you would want to record with higher sample rates and bit depths. There are reasons why you would want to stay at that higher resolution when you’re bouncing files that will be imported into another session for further processing as well. But when it comes to bouncing the final track, it’s evident that the frequency range and dynamic range that the 44.1kHz, 16 bit standard is capable of producing is more than adequate. That said, there are those who believe that they can hear an improvement with a higher resolution audio file. For me, CD quality is perfect for the final bounce. But if you’re not convinced, then why not run some tests for your self. Bounce a CD quality file and a higher resolution version and then have a friend blind test you to see if you can hear a difference.

Using dither when you bounce audio:

Before we move on to some of the other common audio bouncing applications, there’s something else that you need to be aware of when bouncing your final track.

Because your final bounce will have a bit depth of either 16 or 24 bit, you’ll need to apply something called ‘dither‘. In some DAW’s, the bounce dialogue will give you the option to apply dither when you bounce your audio. If not, you will need to add it via a plugin. This plugin should be the very last plugin that your audio passes through. As a rule, dither is required whenever you bounce either a 16 or 24 bit file. The only time you don’t need to apply dither is when you bounce to 32 bit floating point. Keep in mind that bouncing to 32 bit float is only appropriate when bouncing audio which will be imported into a DAW. It is not to be used as the bit depth for the final mastered track that you will release.

Now, let’s look at some other occasions when you’ll need to bounce the audio in your session…

How do you bounce audio for mastering?

The final step in the production of a track, which comes after mixing, is mastering. Once you’ve mixed your track, you’ll need to bounce your mix so that it can be imported into a mastering session (or sent off to a mastering engineer). The file types most commonly used for this are WAV and AIFF as these are both lossless formats.

To bounce your track for mastering, keep your bit depth and sample rate the same as they currently are. You can convert to a lower sample rate and bit depth later when you bounce the final mastered track if you need to. Or alternatively, you can bounce a 32 bit floating point file (providing your mastering engineer accepts this). The benefit of bouncing to 32 bit floating point is that if there is any clipping in the track, the track can be turned down in the mastering session and can still be used. That said, best practice dictates that you should leave about 6dB of headroom in your mix for the mastering stage. So, providing you’ve done this, bouncing to your original bit depth should be fine.

If you’re bouncing to either 16 or 24 bit, you need to apply dither. If you’re bouncing to 32 bit floating point, you don’t. As previously mentioned, real time bouncing is the most reliable process. You’ll also want to set your format to stereo-interleaved.

Bouncing audio for stem mastering:

A variation on the traditional mastering process, which involves the mastering of your mix as a single stereo file, is a process called stem mastering. Once your track is mixed and ready to be mastered, rather than bouncing the entire mix, you instead bounce each different group of instruments to individual tracks or ‘stems’. This gives you more control over the processing that is applied to each group of instruments at the mastering stage.

Typical groups of instruments that would form the stems would be: drums, bass, acoustic guitars, electric guitars, synths, vocals etc. Some mastering engineers request certain things like the lead vocal or the kick drum as separate stems too. All automation, processing and effects should be printed into the stems when you bounce. That way, when all of the stems are imported into a session, they form your exact mix. Keep your sample rate and bit depth the same, or bounce to 32 bit floating point. Apply dither if you’re saving to 16 or 24 bit. Don’t use dither if you’re saving to 32 bit float. Bounce WAV or AIFF files in stereo interleaved format, and remember to leave 6dB of headroom.

Finally, if you’re sending the stems to a mastering engineer, check which file type they prefer and whether they accept 32 bit float files if that’s what you intend to send.

Other bouncing applications:

There are times when you may want to bounce audio for reasons other than the ones covered so far. A common process in analogue recording studios was to bounce down multiple tracks, like all of the drum tracks for example, to free up space for more tracks to be recorded on the tape machine which had only a limited number of tracks available. This could also be done to capture the sound of tracks being processed through a piece of outboard gear like a compressor or a reverb, so that it could be freed up for use with a different track.

That said, with huge track counts and the ability to use endless amounts of plugins in modern DAW’s, these factors are now less of a consideration. But there are still times when this process could come in handy. An example of this would be to free up CPU power by replacing several tracks and their plugins with a single track with the processing or effects baked in. Of course, the downside is that individual levels of those multiple tracks can no longer be altered after the bounce.

Conclusion:

The correct settings to use when you bounce audio can seem daunting at first. Things are made even trickier when you consider the fact that the correct settings for you to use change depending on why it is that you’re bouncing your audio. Just refer to this lesson anytime you need to and you’ll get a perfect bounce every time.

At what stages in the production process do you typically bounce down your audio? Leave your thoughts in the comment section below.

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