The output WAV can be larger than the source files because Audio Joiner creates a new, uncompressed PCM16 recording rather than preserving the compressed codecs used by the inputs. A compressed MP3, AAC, Opus, Vorbis, or FLAC file can occupy much less space than the decoded audio stored as 16-bit PCM samples.
The increase is not caused by a transition being inserted at each join. Audio Joiner concatenates decoded channel samples directly: the last sample frame of one track is followed immediately by the first sample frame of the next. It adds no silence, overlap, crossfade, normalization, transition, or automatic trimming. When the resulting WAV expands, the main factors are its storage format, decoded sample rate, channel count, and combined duration.
Why the joined WAV grows
Compressed audio uses a codec to represent the original recording with less stored data. PCM16 takes a different approach: it stores a signed 16-bit value for every sample in every channel. Joining files combines their decoded durations into one continuous PCM payload, so several individually compact compressed files can produce a much larger WAV.
The problem is not simply the word “WAV.” A WAV file is a container, and different files placed inside it can use different forms of encoding. Audio Joiner specifically creates a RIFF/WAVE file containing uncompressed, signed 16-bit PCM. It does not retain the inputs’ original codec, bitrate, or encoder settings.
What determines the output size
For the PCM audio payload, the practical relationship is: decoded duration multiplied by decoded sample rate multiplied by channel count multiplied by two bytes per sample. The tool then adds a 44-byte RIFF/WAVE header.
| Factor | Source files | Joined WAV from Audio Joiner |
|---|---|---|
| Encoding | May use a compressed codec or uncompressed PCM | Always encoded as uncompressed PCM16 |
| Sample storage | Depends on the source codec | Every decoded channel sample uses 16 bits |
| Sample rate | Each file can have its own stored rate | Uses the shared decoding context’s resulting rate |
| Channels | Individual files may have different channel layouts | Every selected track must decode to the same channel count |
| Join boundaries | Separate files have separate beginnings and endings | Decoded frames are joined directly without inserted audio |
| Metadata | May contain tags, album art, chapters, or other fields | Original container metadata is not preserved |
Although its PCM payload would be 115,200,000 bytes, a 10-minute stereo recording at 48,000 samples per second would require 57,600,000 samples across both channels, exceeding the 30,000,000-sample limit, so Audio Joiner would reject it rather than produce the WAV. The actual Audio Joiner result uses the decoded rate, channel count, and duration shown for the selection.
Why resampling can change the total
Browser decoding does not necessarily preserve the sample rate stored in each source. Audio Joiner decodes every selected file through the same AudioContext, and that context may resample the files to one working rate. The displayed track and result rate can therefore differ from the rates in the original files. The output cannot preserve independent source sample rates.
Resampling can push the PCM size up or down. If the shared working rate is higher than an original file’s rate, more sample frames are stored; if it is lower, fewer are stored. The difference caused by replacing compressed audio with PCM usually remains the dominant factor, however. The final size should be judged from the decoded duration and rate rather than estimated from the original compressed bitrate.
Channel count matters in the same way. All decoded tracks must have the same number of channels. A mixture of mono and stereo files is rejected instead of silently duplicating, dropping, averaging, or remapping channels. For a successful join, matching channels are retained in their decoded order and interleaved into the final WAV.
Check compatibility and selection limits
The file picker recognizes common MP3, WAV, M4A, AAC, Ogg, WebM, and FLAC names and MIME types. A recognized extension does not guarantee that every codec variant can be decoded by the current browser and operating system. Audio Joiner relies on the browser’s Web Audio API rather than adding a codec library or server fallback. Damaged, encrypted, incomplete, mislabeled, or unsupported files produce an error. The MDN decodeAudioData reference and AudioBuffer reference explain the browser decoding and decoded-buffer properties involved.
Before joining, check every interacting limit:
| Selection item | Supported limit |
|---|---|
| Number of files | 2–10 |
| Each encoded input file | No larger than 25 MiB, or 26,214,400 bytes |
| Combined encoded inputs | No more than 100 MiB, or 104,857,600 bytes |
| Total decoded duration | No more than 30 minutes |
| Decoded sample rate | No more than 192 kHz |
| Decoded channel count | No more than eight channels, with the same count required for every selected track |
| Total decoded samples | No more than 30 million, counted across all channels |
A high-rate or multichannel selection can reach the sample budget before it reaches the duration limit. Audio Joiner does not shorten, downmix, downsample, or omit content to make a selection fit. It rejects the selection with a specific message instead.
Join the files in the order you want
- Open Audio Joiner and select 2–10 browser-decodable audio files together. Confirm that the selection satisfies the displayed per-file and total input limits.
- Wait for the browser to decode the files. Preview every decoded track, then use Move up or Move down until the visible list matches the required sequence.
- Select Join in this order and preview the resulting PCM16 WAV before saving it.
- Download the WAV, but keep the source files until you have confirmed the downloaded duration, track order, joins, channel playback, and file size. If a check fails, replace or reorder the selection and join it again.
File reading, decoding, concatenation, WAV encoding, preview, and download all happen in the current browser tab, so the source files are not uploaded. Selected files and the finished WAV use temporary local object URLs, which are released when they are replaced or the page closes.
What the new WAV preserves—and what it does not
The download is a newly encoded RIFF/WAVE file with interleaved, little-endian, signed 16-bit PCM samples. Its header records the channel count, decoded sample rate, byte rate, block alignment, 16-bit depth, and exact data length. The join preserves the selected order and matching channel identity, but it creates a static PCM representation rather than carrying the source containers forward.
As a result, the output does not preserve the original codec, bitrate, encoder settings, tags, album art, chapters, cue points, loop points, loudness fields, timestamps, or other container metadata. The absence of those fields does not explain the larger size; the expanded PCM audio payload does.
Keep the result manageable
The 100 MiB total input limit applies to the encoded files you select, not to the size of the resulting WAV. The 30,000,000-channel-sample cap limits an accepted PCM16 WAV to 60,000,044 bytes including its header, about 57.2 MiB, so it cannot exceed 100 MiB. Review the decoded duration, rate, and channel count before joining because those values determine the final payload much more closely than the original file sizes do.
Audio Joiner always exports PCM16 WAV, so it does not provide a compressed-output option when storage efficiency is the priority. A dedicated editor is the appropriate choice when you need compressed delivery, metadata preservation, fades, loudness matching, channel conversion, or sample-level repair. If you only need a particular time range rather than a complete track, Audio Cutter provides that focused workflow before the resulting WAV is joined.
For a deeper look, see Cut Audio Files Online: Trim Exact Ranges to WAV.
For a deeper look, see Audio Joiner App: Join Clips Locally Into One WAV.